Semi invisible lockfile undeletable

I use netxcloud for my personal datacloud. Server on Linux, clients on Linux, Windows 7/10, Android and IOS.
On my Linux desktop is VirtualBox installed with a virtual Windows 10 with Autodesk Inventor. This virutal Windows uses my cloud through samba fileshare to linux desktop.
Everything works just great.

Except, two weeks ago I used this Inventor. It creates a lockfile (lockfile.lck). I shut down Inventor and the virutal Windows correctly. But this lockfile was stored on the cloud (I see it when I look with the webinterface).

The Linux client reports a sync error meaning it cannot sync this file. Strangely enough the other clients don’t see this file and don’t want to sync it of course. The sync error is really annoying, it comes back every so many minutes.

So this file is not on any client. It is on the cloud (as I see through webinterface), and it caused errors in the Linux client, but not on any other client.
I tried to delete it through the webinterface, but that gives an error, and the file stays in place.

Does anybody have any idea how to resolve this?


Which error?

Which server environment?
Have you checked file permissions/attributes on Server?

Sorry for my slow reactions, I had some exams to do.
The server is a Ubuntu (kubuntu) 18.04.
Nextcloud server software is 14.0.1
Nextclout client software is 2.3.3 (on Linux)
The file exists in the database, shows in the webinterface. The file doesn’t show up in any client.
The sync process produces the errormessage:

: Server replied: Locked (" is locked")

If I log in through webinterface, I see the file, when I try to delete it, I get the errormessage "Error deleting " when I try to move it, a similar message "Could not move ".

When I go into the nextcloud data, ("/opt/nextcloud/data//files/, the file doesn’t exist there either. So I guess a database mismatch. How to repair this? Through mysqladmin?

How did you go there and checked for file?
Maybe your explorer is hiding system files?

I used in this case Dolphin (kde) as root. No hidden files.
This morning I looked again on the Internet, found a few threads about file locking in Nextcloud (and Owncloud). I disabled file locking in Nextcloud through config.php, and rebooted the system. Until now the error stays away.
In the mean time I also browsed through de sql interface (MysqlAdmin), and I saw in nextcloud the table “oc_file_locks”. In there some 25 records only with cryptic references (no file names). I try to delete them (after the reboot), but they reappear (with new id). So I think this is weird, no file-locking and still persistent file_lock records?
But anyway, at this point everything is OK, I will try to upgrade the software this holiday, and we’ll see whether it happens again or not.

Thanks for your help.