diff --git a/lib/ACL/ACLManager.php b/lib/ACL/ACLManager.php
index 602ae58b0..84baf570c 100644
--- a/lib/ACL/ACLManager.php
+++ b/lib/ACL/ACLManager.php
@@ -15,6 +15,7 @@
 use OCP\Files\IRootFolder;
 use OCP\IUser;
 use Psr\Log\LoggerInterface;
+use RuntimeException;
 
 class ACLManager {
 	private CappedMemoryCache $ruleCache;
@@ -97,6 +98,9 @@ private function getRelevantPaths(string $path): array {
 			$groupFolderId = (int)$groupFolderId;
 			/* Remove the date part */
 			$separatorPos = strrpos($rootTrashedItemName, '.d');
+			if ($separatorPos === false) {
+				throw new RuntimeException('Invalid trash item name ' . $rootTrashedItemName);
+			}
 			$rootTrashedItemDate = (int)substr($rootTrashedItemName, $separatorPos + 2);
 			$rootTrashedItemName = substr($rootTrashedItemName, 0, $separatorPos);
 		}
@@ -105,6 +109,7 @@ private function getRelevantPaths(string $path): array {
 			$path = dirname($path);
 			if ($fromTrashbin && ($path === '__groupfolders/trash')) {
 				/* We are in trash and hit the root folder, continue looking for ACLs on parent folders in original location */
+				/** @psalm-suppress PossiblyUndefinedVariable Variables are defined above */
 				$trashItemRow = $this->trashManager->getTrashItemByFileName($groupFolderId, $rootTrashedItemName, $rootTrashedItemDate);
 				$fromTrashbin = false;
 				if ($trashItemRow) {
diff --git a/lib/ACL/ACLStorageWrapper.php b/lib/ACL/ACLStorageWrapper.php
index b80948a85..1d449a0f4 100644
--- a/lib/ACL/ACLStorageWrapper.php
+++ b/lib/ACL/ACLStorageWrapper.php
@@ -96,6 +96,10 @@ public function opendir($path) {
 		}
 
 		$handle = parent::opendir($path);
+		if ($handle === false) {
+			return false;
+		}
+
 		$items = [];
 		while (($file = readdir($handle)) !== false) {
 			if ($file !== '.' && $file !== '..') {
diff --git a/lib/Mount/GroupMountPoint.php b/lib/Mount/GroupMountPoint.php
index ee02ba8b8..9261711a6 100644
--- a/lib/Mount/GroupMountPoint.php
+++ b/lib/Mount/GroupMountPoint.php
@@ -7,6 +7,7 @@
 namespace OCA\GroupFolders\Mount;
 
 use OC\Files\Mount\MountPoint;
+use OC\Files\Storage\Storage;
 use OCP\Files\Mount\ISystemMountPoint;
 
 class GroupMountPoint extends MountPoint implements ISystemMountPoint {
diff --git a/lib/Mount/MountProvider.php b/lib/Mount/MountProvider.php
index edada0aa9..83030c6d0 100644
--- a/lib/Mount/MountProvider.php
+++ b/lib/Mount/MountProvider.php
@@ -215,6 +215,9 @@ public function getMount(
 				return null;
 			}
 			$cacheEntry = $this->getRootFolder()->getStorage()->getCache()->get($folder->getId());
+			if ($cacheEntry === false) {
+				return null;
+			}
 		}
 
 		$storage = $this->getRootFolder()->getStorage();
diff --git a/psalm.xml b/psalm.xml
index 7d4074c62..76d8dd4da 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -4,7 +4,7 @@
   - SPDX-License-Identifier: AGPL-3.0-or-later
 -->
 <psalm
-		errorLevel="4"
+		errorLevel="3"
 		resolveFromConfigFile="true"
 		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 		xmlns="https://getpsalm.org/schema/config"