diff --git a/lib/private/Files/Config/UserMountCache.php b/lib/private/Files/Config/UserMountCache.php
index 6c64dc4973f..8275eee7b9f 100644
--- a/lib/private/Files/Config/UserMountCache.php
+++ b/lib/private/Files/Config/UserMountCache.php
@@ -251,6 +251,9 @@ class UserMountCache implements IUserMountCache {
 	 */
 	public function getMountsForUser(IUser $user) {
 		$userUID = $user->getUID();
+		if (!$this->userManager->userExists($userUID)) {
+			return [];
+		}
 		if (!isset($this->mountsForUsers[$userUID])) {
 			$builder = $this->connection->getQueryBuilder();
 			$query = $builder->select('storage_id', 'root_id', 'user_id', 'mount_point', 'mount_id', 'mount_provider_class')
@@ -370,14 +373,18 @@ class UserMountCache implements IUserMountCache {
 		}
 		$mountsForStorage = $this->getMountsForStorageId($storageId, $user);
 
-		// filter mounts that are from the same storage but a different directory
+		// filter mounts that are from the same storage but not a parent of the file we care about
 		$filteredMounts = array_filter($mountsForStorage, function (ICachedMountInfo $mount) use ($internalPath, $fileId) {
 			if ($fileId === $mount->getRootId()) {
 				return true;
 			}
 			$internalMountPath = $mount->getRootInternalPath();
 
-			return $internalMountPath === '' || substr($internalPath, 0, strlen($internalMountPath) + 1) === $internalMountPath . '/';
+			return $internalMountPath === '' || str_starts_with($internalPath, $internalMountPath . '/');
+		});
+
+		$filteredMounts = array_filter($filteredMounts, function (ICachedMountInfo $mount) {
+			return $this->userManager->userExists($mount->getUser()->getUID());
 		});
 
 		return array_map(function (ICachedMountInfo $mount) use ($internalPath) {
diff --git a/tests/lib/Files/Config/UserMountCacheTest.php b/tests/lib/Files/Config/UserMountCacheTest.php
index 10984e1d578..9e910f4f47f 100644
--- a/tests/lib/Files/Config/UserMountCacheTest.php
+++ b/tests/lib/Files/Config/UserMountCacheTest.php
@@ -137,7 +137,7 @@ class UserMountCacheTest extends TestCase {
 		$this->assertCount(1, $cachedMounts);
 		$cachedMount = $cachedMounts[$this->keyForMount($mount)];
 		$this->assertEquals('/asd/', $cachedMount->getMountPoint());
-		$this->assertEquals($user, $cachedMount->getUser());
+		$this->assertEquals($user->getUID(), $cachedMount->getUser()->getUID());
 		$this->assertEquals($storage->getCache()->getId(''), $cachedMount->getRootId());
 		$this->assertEquals($storage->getStorageCache()->getNumericId(), $cachedMount->getStorageId());
 	}
@@ -161,7 +161,7 @@ class UserMountCacheTest extends TestCase {
 		$this->assertCount(1, $cachedMounts);
 		$cachedMount = $cachedMounts[$this->keyForMount($mount)];
 		$this->assertEquals('/asd/', $cachedMount->getMountPoint());
-		$this->assertEquals($user, $cachedMount->getUser());
+		$this->assertEquals($user->getUID(), $cachedMount->getUser()->getUID());
 		$this->assertEquals($storage->getCache()->getId(''), $cachedMount->getRootId());
 		$this->assertEquals($storage->getStorageCache()->getNumericId(), $cachedMount->getStorageId());
 	}
@@ -253,13 +253,13 @@ class UserMountCacheTest extends TestCase {
 
 		$this->assertCount(2, $cachedMounts);
 		$this->assertEquals('/foo/', $cachedMounts[$this->keyForMount($mount1)]->getMountPoint());
-		$this->assertEquals($user1, $cachedMounts[$this->keyForMount($mount1)]->getUser());
+		$this->assertEquals($user1->getUID(), $cachedMounts[$this->keyForMount($mount1)]->getUser()->getUID());
 		$this->assertEquals($id1, $cachedMounts[$this->keyForMount($mount1)]->getRootId());
 		$this->assertEquals(1, $cachedMounts[$this->keyForMount($mount1)]->getStorageId());
 		$this->assertEquals('', $cachedMounts[$this->keyForMount($mount1)]->getRootInternalPath());
 
 		$this->assertEquals('/bar/', $cachedMounts[$this->keyForMount($mount2)]->getMountPoint());
-		$this->assertEquals($user1, $cachedMounts[$this->keyForMount($mount2)]->getUser());
+		$this->assertEquals($user1->getUID(), $cachedMounts[$this->keyForMount($mount2)]->getUser()->getUID());
 		$this->assertEquals($id2, $cachedMounts[$this->keyForMount($mount2)]->getRootId());
 		$this->assertEquals(2, $cachedMounts[$this->keyForMount($mount2)]->getStorageId());
 		$this->assertEquals('foo/bar', $cachedMounts[$this->keyForMount($mount2)]->getRootInternalPath());
@@ -288,12 +288,12 @@ class UserMountCacheTest extends TestCase {
 		$this->assertCount(2, $cachedMounts);
 
 		$this->assertEquals('/bar/', $cachedMounts[0]->getMountPoint());
-		$this->assertEquals($user1, $cachedMounts[0]->getUser());
+		$this->assertEquals($user1->getUID(), $cachedMounts[0]->getUser()->getUID());
 		$this->assertEquals($id2, $cachedMounts[0]->getRootId());
 		$this->assertEquals(2, $cachedMounts[0]->getStorageId());
 
 		$this->assertEquals('/bar/', $cachedMounts[1]->getMountPoint());
-		$this->assertEquals($user2, $cachedMounts[1]->getUser());
+		$this->assertEquals($user2->getUID(), $cachedMounts[1]->getUser()->getUID());
 		$this->assertEquals($id2, $cachedMounts[1]->getRootId());
 		$this->assertEquals(2, $cachedMounts[1]->getStorageId());
 	}
@@ -318,12 +318,12 @@ class UserMountCacheTest extends TestCase {
 		$this->assertCount(2, $cachedMounts);
 
 		$this->assertEquals('/bar/', $cachedMounts[0]->getMountPoint());
-		$this->assertEquals($user1, $cachedMounts[0]->getUser());
+		$this->assertEquals($user1->getUID(), $cachedMounts[0]->getUser()->getUID());
 		$this->assertEquals($id2, $cachedMounts[0]->getRootId());
 		$this->assertEquals(2, $cachedMounts[0]->getStorageId());
 
 		$this->assertEquals('/bar/', $cachedMounts[1]->getMountPoint());
-		$this->assertEquals($user2, $cachedMounts[1]->getUser());
+		$this->assertEquals($user2->getUID(), $cachedMounts[1]->getUser()->getUID());
 		$this->assertEquals($id2, $cachedMounts[1]->getRootId());
 		$this->assertEquals(2, $cachedMounts[1]->getStorageId());
 	}
@@ -378,7 +378,7 @@ class UserMountCacheTest extends TestCase {
 		$this->assertCount(1, $cachedMounts);
 
 		$this->assertEquals('/foo/', $cachedMounts[0]->getMountPoint());
-		$this->assertEquals($user1, $cachedMounts[0]->getUser());
+		$this->assertEquals($user1->getUID(), $cachedMounts[0]->getUser()->getUID());
 		$this->assertEquals($rootId, $cachedMounts[0]->getRootId());
 		$this->assertEquals(2, $cachedMounts[0]->getStorageId());
 	}
@@ -400,7 +400,7 @@ class UserMountCacheTest extends TestCase {
 		$this->assertCount(1, $cachedMounts);
 
 		$this->assertEquals('/foo/', $cachedMounts[0]->getMountPoint());
-		$this->assertEquals($user1, $cachedMounts[0]->getUser());
+		$this->assertEquals($user1->getUID(), $cachedMounts[0]->getUser()->getUID());
 		$this->assertEquals($rootId, $cachedMounts[0]->getRootId());
 		$this->assertEquals(2, $cachedMounts[0]->getStorageId());
 		$this->assertEquals('foo/bar', $cachedMounts[0]->getInternalPath());
@@ -433,7 +433,7 @@ class UserMountCacheTest extends TestCase {
 		$this->assertCount(1, $cachedMounts);
 
 		$this->assertEquals('/', $cachedMounts[0]->getMountPoint());
-		$this->assertEquals($user1, $cachedMounts[0]->getUser());
+		$this->assertEquals($user1->getUID(), $cachedMounts[0]->getUser()->getUID());
 		$this->assertEquals($folderId, $cachedMounts[0]->getRootId());
 		$this->assertEquals(2, $cachedMounts[0]->getStorageId());
 		$this->assertEquals('foo', $cachedMounts[0]->getRootInternalPath());