diff -ur clean/html/apps/files_versions/lib/Listener/FileEventsListener.php patched/html/apps/files_versions/lib/Listener/FileEventsListener.php
--- clean/html/apps/files_versions/lib/Listener/FileEventsListener.php	2024-09-13 16:04:38.000000000 +0100
+++ patched/html/apps/files_versions/lib/Listener/FileEventsListener.php	2024-09-13 13:20:40.000000000 +0100
@@ -381,6 +381,26 @@
 			}
 		}
 

+		// If we are writing to a shared file that this user does not have access to, for
+		// instance when filling in a form on group storage with an attached spreadsheet,
+		// both $user and $owner will be the current UID, and the file may not be
+		// accessible from either. Try getting it from the path.
+		//
+		// Note that this is safe because this is a versioning hook: we must have already
+		// checked that the user has access to the file elsewhere in the code.
+
+		if ($owner == $user)
+		{
+			$parts = explode ('/', $node->getPath());
+			if (count ($parts) > 1) {
+				$oldOwner = $owner;
+				$owner = $parts[1];
+				$this->logger->warning("Assuming owner is actually ".$owner." not ".$oldOwner." for ".($node->getPath()));
+			}
+			$path = $this->rootFolder
+				->getUserFolder($owner)
+				->getRelativePath($node->getPath());
+
+			if ($path !== null) {
+				$this->logger->warning("Found path with fallback owner: ".$path);
+				return $path;
+			}
+		}
+
 		return null;
 	}
 }