diff --git a/lib/Service/CachedRequestService.php b/lib/Service/CachedRequestService.php
index 8437310d31..f9e6b83627 100644
--- a/lib/Service/CachedRequestService.php
+++ b/lib/Service/CachedRequestService.php
@@ -42,11 +42,19 @@ public function get(): ?string {
 			return $cached;
 		}
 
-		$folder = $this->getAppDataFolder();
-		if ($folder->fileExists($this->cacheKey)) {
-			$value = $folder->getFile($this->cacheKey)->getContent();
-			$cache->set($this->cacheKey, $value, 3600);
-			return $value;
+		try {
+			$folder = $this->getAppDataFolder();
+			if ($folder->fileExists($this->cacheKey)) {
+				$value = $folder->getFile($this->cacheKey)->getContent();
+				try {
+					$cache->set($this->cacheKey, $value, 3600);
+				} catch (\Throwable $e) {
+					$this->logger->warning('Could not write remote data to cache for ' . $this->cacheKey, ['exception' => $e]);
+				}
+				return $value;
+			}
+		} catch (\Throwable $e) {
+			$this->logger->warning('Could not read cached remote data for ' . $this->cacheKey, ['exception' => $e]);
 		}
 
 		return null;
@@ -83,9 +91,14 @@ public function fetch(): string {
 	public function resetCache(): void {
 		$cache = $this->cacheFactory->createDistributed('richdocuments');
 		$cache->remove($this->cacheKey);
-		$folder = $this->getAppDataFolder();
-		if ($folder->fileExists($this->cacheKey)) {
-			$folder->getFile($this->cacheKey)->delete();
+
+		try {
+			$folder = $this->getAppDataFolder();
+			if ($folder->fileExists($this->cacheKey)) {
+				$folder->getFile($this->cacheKey)->delete();
+			}
+		} catch (\Throwable $e) {
+			$this->logger->warning('Could not remove cached remote data for ' . $this->cacheKey, ['exception' => $e]);
 		}
 	}
 
diff --git a/lib/Service/DiscoveryService.php b/lib/Service/DiscoveryService.php
index 9a001b39a8..7f52dd95ec 100644
--- a/lib/Service/DiscoveryService.php
+++ b/lib/Service/DiscoveryService.php
@@ -120,8 +120,13 @@ public function getProofKeyOld(): ?ProofKey {
 	}
 
 	private function getParsed(): SimpleXMLElement {
+		$raw = $this->get();
+		if ($raw === null) {
+			throw new \Exception('No discovery data available');
+		}
+
 		try {
-			return new SimpleXMLElement($this->get());
+			return new SimpleXMLElement($raw);
 		} catch (\Exception $e) {
 			$this->logger->error($e->getMessage());
 			throw new \Exception('Could not parse discovery XML');
diff --git a/lib/WOPI/Parser.php b/lib/WOPI/Parser.php
index 632a2ca7e1..4852f9d951 100644
--- a/lib/WOPI/Parser.php
+++ b/lib/WOPI/Parser.php
@@ -36,8 +36,15 @@ public function getUrlSrcValue(string $appName): string {
 	 */
 	private function getUrlSrc(string $mimetype): array {
 		$discovery = $this->discoveryService->get();
+		if ($discovery === null) {
+			throw new Exception('No discovery data available');
+		}
+
 		$this->logger->debug('WOPI::getUrlSrc discovery: {discovery}', ['discovery' => $discovery]);
 		$discoveryParsed = simplexml_load_string($discovery);
+		if ($discoveryParsed === false) {
+			throw new Exception('Could not parse WOPI discovery response');
+		}
 
 		$result = $discoveryParsed->xpath(sprintf('/wopi-discovery/net-zone/app[@name=\'%s\']/action', $mimetype));
 		if ($result && count($result) > 0) {
diff --git a/tests/lib/Service/CachedRequestServiceTest.php b/tests/lib/Service/CachedRequestServiceTest.php
index 970be415dd..8ba49088c2 100644
--- a/tests/lib/Service/CachedRequestServiceTest.php
+++ b/tests/lib/Service/CachedRequestServiceTest.php
@@ -11,7 +11,10 @@
 
 use OCA\Richdocuments\Service\CachedRequestService;
 use OCP\Files\AppData\IAppDataFactory;
+use OCP\Files\GenericFileException;
 use OCP\Files\IAppData;
+use OCP\Files\NotFoundException;
+use OCP\Files\NotPermittedException;
 use OCP\Files\SimpleFS\ISimpleFile;
 use OCP\Files\SimpleFS\ISimpleFolder;
 use OCP\Http\Client\IClient;
@@ -118,6 +121,80 @@ public function testGetReturnsFileValueIfCacheMiss(): void {
 		$this->assertEquals('from-file', $result);
 	}
 
+	public function testGetReturnsFileValueIfCachingTheValueFails(): void {
+		$this->cache->expects($this->once())
+			->method('get')
+			->with('unittest-cachekey')
+			->willReturn(null);
+		$this->folder->expects($this->once())
+			->method('fileExists')
+			->with('unittest-cachekey')
+			->willReturn(true);
+		$this->folder->expects($this->once())
+			->method('getFile')
+			->with('unittest-cachekey')
+			->willReturn($this->file);
+		$this->file->expects($this->once())
+			->method('getContent')
+			->willReturn('from-file');
+		$this->cache->expects($this->once())
+			->method('set')
+			->with('unittest-cachekey', 'from-file', 3600)
+			->willThrowException(new \RuntimeException('Distributed cache unavailable'));
+		$this->logger->expects($this->once())->method('warning');
+
+		$this->assertEquals('from-file', $this->service->get());
+	}
+
+	public function testGetReturnsNullIfCachedFileIsUnreadable(): void {
+		$this->cache->expects($this->once())
+			->method('get')
+			->with('unittest-cachekey')
+			->willReturn(null);
+		$this->folder->expects($this->once())
+			->method('fileExists')
+			->with('unittest-cachekey')
+			->willReturn(true);
+		$this->folder->expects($this->once())
+			->method('getFile')
+			->with('unittest-cachekey')
+			->willReturn($this->file);
+		$this->file->expects($this->once())
+			->method('getContent')
+			->willThrowException(new GenericFileException());
+		$this->cache->expects($this->never())->method('set');
+		$this->logger->expects($this->once())->method('warning');
+
+		$this->assertNull($this->service->get());
+	}
+
+	public function testGetReturnsNullIfAppDataFolderIsUnavailable(): void {
+		$appData = $this->createMock(IAppData::class);
+		$appData->method('getFolder')->willThrowException(new NotFoundException());
+		$appData->method('newFolder')->willThrowException(new \RuntimeException('appdata unavailable'));
+
+		$appDataFactory = $this->createMock(IAppDataFactory::class);
+		$appDataFactory->method('get')->willReturn($appData);
+
+		$service = new TestCachedRequestService(
+			$this->clientService,
+			$this->cacheFactory,
+			$appDataFactory,
+			$this->appConfig,
+			$this->logger,
+			'unittest-cachekey'
+		);
+
+		$this->cache->expects($this->once())
+			->method('get')
+			->with('unittest-cachekey')
+			->willReturn(null);
+		$this->cache->expects($this->never())->method('set');
+		$this->logger->expects($this->once())->method('warning');
+
+		$this->assertNull($service->get());
+	}
+
 	public function testResetCacheRemovesCacheAndFile(): void {
 		$this->cache->expects($this->once())->method('remove')->with('unittest-cachekey');
 		$this->folder->method('fileExists')->with('unittest-cachekey')->willReturn(true);
@@ -128,6 +205,19 @@ public function testResetCacheRemovesCacheAndFile(): void {
 		$this->assertTrue(true); // No exceptions thrown
 	}
 
+	public function testResetCacheWhenCachedFileCannotBeRemoved(): void {
+		$this->cache->expects($this->once())->method('remove')->with('unittest-cachekey');
+		$this->folder->method('fileExists')->with('unittest-cachekey')->willReturn(true);
+		$this->folder->method('getFile')->with('unittest-cachekey')->willReturn($this->file);
+		$this->file->expects($this->once())
+			->method('delete')
+			->willThrowException(new NotPermittedException());
+		$this->logger->expects($this->once())->method('warning');
+
+		$this->service->resetCache();
+		$this->assertTrue(true); // No exceptions thrown
+	}
+
 	public function testGetLastUpdateReturnsMTimeIfFileExists(): void {
 		$this->folder->expects($this->once())
 			->method('fileExists')
diff --git a/tests/lib/Service/CapabilitiesServiceTest.php b/tests/lib/Service/CapabilitiesServiceTest.php
index 1b9b2cb1a3..67a1349f98 100644
--- a/tests/lib/Service/CapabilitiesServiceTest.php
+++ b/tests/lib/Service/CapabilitiesServiceTest.php
@@ -12,7 +12,9 @@
 use OCA\Richdocuments\Service\CapabilitiesService;
 use OCP\App\IAppManager;
 use OCP\Files\AppData\IAppDataFactory;
+use OCP\Files\GenericFileException;
 use OCP\Files\IAppData;
+use OCP\Files\SimpleFS\ISimpleFile;
 use OCP\Files\SimpleFS\ISimpleFolder;
 use OCP\Http\Client\IClient;
 use OCP\Http\Client\IClientService;
@@ -62,4 +64,40 @@ public function testFetchRefreshesCapabilities(): void {
 		$service->fetch();
 		$this->assertSame('2.0', $service->getProductVersion());
 	}
+
+	public function testGetCapabilitiesWithUnreadableCachedFile(): void {
+		$cache = $this->createStub(ICache::class);
+		$cache->method('get')->willReturn(null);
+		$cacheFactory = $this->createStub(ICacheFactory::class);
+		$cacheFactory->method('createDistributed')->willReturn($cache);
+
+		$file = $this->createStub(ISimpleFile::class);
+		$file->method('getContent')->willThrowException(new GenericFileException());
+		$folder = $this->createStub(ISimpleFolder::class);
+		$folder->method('fileExists')->willReturn(true);
+		$folder->method('getFile')->willReturn($file);
+
+		$appData = $this->createStub(IAppData::class);
+		$appData->method('getFolder')->willReturn($folder);
+		$appDataFactory = $this->createStub(IAppDataFactory::class);
+		$appDataFactory->method('get')->willReturn($appData);
+
+		$config = $this->createStub(IConfig::class);
+		$config->method('getAppValue')->willReturn('https://collabora.example');
+
+		$service = new CapabilitiesService(
+			$this->createStub(IClientService::class),
+			$cacheFactory,
+			$appDataFactory,
+			$this->createStub(IAppConfig::class),
+			$this->createStub(LoggerInterface::class),
+			$config,
+			$this->createStub(IAppManager::class),
+			$this->createStub(IL10N::class),
+		);
+
+		$this->assertSame([], $service->getCapabilities());
+		$this->assertNull($service->getProductVersion());
+		$this->assertFalse($service->hasTemplateSource());
+	}
 }
diff --git a/tests/lib/Service/DiscoveryServiceTest.php b/tests/lib/Service/DiscoveryServiceTest.php
index 1de4bd90b6..6df13095e1 100644
--- a/tests/lib/Service/DiscoveryServiceTest.php
+++ b/tests/lib/Service/DiscoveryServiceTest.php
@@ -93,6 +93,27 @@ public function testGetProofKey(): void {
 		$this->assertEquals('world', $proofKey->getExponent());
 	}
 
+	public function testHasProofKeyWithoutDiscoveryData(): void {
+		$this->discoveryService->method('get')
+			->willReturn(null);
+
+		$this->assertFalse($this->discoveryService->hasProofKey());
+	}
+
+	public function testGetProofKeyWithoutDiscoveryData(): void {
+		$this->discoveryService->method('get')
+			->willReturn(null);
+
+		$this->assertNull($this->discoveryService->getProofKey());
+	}
+
+	public function testGetProofKeyOldWithoutDiscoveryData(): void {
+		$this->discoveryService->method('get')
+			->willReturn(null);
+
+		$this->assertNull($this->discoveryService->getProofKeyOld());
+	}
+
 	public function testGetProofKeyOld(): void {
 		$discoveryXml = <<<END
         <wopi-discovery>
diff --git a/tests/lib/WOPI/ParserTest.php b/tests/lib/WOPI/ParserTest.php
new file mode 100644
index 0000000000..f0c5a38cfb
--- /dev/null
+++ b/tests/lib/WOPI/ParserTest.php
@@ -0,0 +1,100 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace Tests\Richdocuments\WOPI;
+
+use Exception;
+use OCA\Richdocuments\Service\DiscoveryService;
+use OCA\Richdocuments\WOPI\Parser;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\LoggerInterface;
+
+class ParserTest extends TestCase {
+	private DiscoveryService&MockObject $discoveryService;
+	private LoggerInterface&MockObject $logger;
+
+	private Parser $parser;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->discoveryService = $this->createMock(DiscoveryService::class);
+		$this->logger = $this->createMock(LoggerInterface::class);
+
+		$this->parser = new Parser($this->discoveryService, $this->logger);
+	}
+
+	public function testGetUrlSrcValue(): void {
+		$discoveryXml = <<<END
+		<wopi-discovery>
+			<net-zone name="external-http">
+				<app name="application/vnd.oasis.opendocument.text">
+					<action name="edit" urlsrc="https://collabora\.example\.com/browser/abc/cool\.html?"/>
+				</app>
+			</net-zone>
+		</wopi-discovery>
+		END;
+
+		$this->discoveryService->method('get')
+			->willReturn($discoveryXml);
+
+		$this->assertEquals(
+			'https://collabora.example.com/browser/abc/cool.html?',
+			$this->parser->getUrlSrcValue('application/vnd.oasis.opendocument.text')
+		);
+	}
+
+	public function testGetUrlSrcValueWithoutDiscoveryData(): void {
+		$this->discoveryService->method('get')
+			->willReturn(null);
+
+		$this->expectException(Exception::class);
+		$this->expectExceptionMessage('No discovery data available');
+
+		$this->parser->getUrlSrcValue('application/vnd.oasis.opendocument.text');
+	}
+
+	public function testGetUrlSrcValueWithUnparseableDiscoveryData(): void {
+		$this->discoveryService->method('get')
+			->willReturn('this is not xml');
+
+		$useInternalErrors = libxml_use_internal_errors(true);
+
+		try {
+			$this->expectException(Exception::class);
+			$this->expectExceptionMessage('Could not parse WOPI discovery response');
+
+			$this->parser->getUrlSrcValue('application/vnd.oasis.opendocument.text');
+		} finally {
+			libxml_clear_errors();
+			libxml_use_internal_errors($useInternalErrors);
+		}
+	}
+
+	public function testGetUrlSrcValueWithUnknownMimetype(): void {
+		$discoveryXml = <<<END
+		<wopi-discovery>
+			<net-zone name="external-http">
+				<app name="application/vnd.oasis.opendocument.text">
+					<action name="edit" urlsrc="https://collabora.example.com/browser/abc/cool.html?"/>
+				</app>
+			</net-zone>
+		</wopi-discovery>
+		END;
+
+		$this->discoveryService->method('get')
+			->willReturn($discoveryXml);
+
+		$this->expectException(Exception::class);
+		$this->expectExceptionMessage('Could not find urlsrc for application/vnd.ms-excel');
+
+		$this->parser->getUrlSrcValue('application/vnd.ms-excel');
+	}
+}