Some files are deleted with filesync

Nextcloud version : 16.0.4
Operating system and version: Ubuntu 18.04
Apache or nginx version: Apache2.4.29
PHP version: 7.2.19

In our company we have a fileserver and a Nextcloud-Server. The fileserver syncs the data with our nextcloud server with the official Client (version 2.5.3) but sometimes some files disappear or get deleted and we see them in the trashcan from the nextcloud. The problem appears randomly and we have no idea what the trigger is. The deleted files are on the fileserver also deleted. The nextcloud Users are synced with an AD via LDAP.

We have the problem since the Install (Nextcloud 14 & Client 1.x) and it didn´t get fixed by updates. We also tried to reinstall the client but it doesn´t helped too.

I don´t know how to replicate the error because we dont see any useful informations in the logs from the nextcloud or the server :confused:

Our question is: What can we do?
Can we see mor detailed Information in the logs or elsewhere?
is it a known bug?
Are there some workarounds?

Thank you for your help. If you need more or more detailed information, I will be happy to provide you with it.

Here are some entries from the nextcloud log:

Fatal	webdav	Sabre\DAV\Exception\BadRequest: expected filesize 2279751 got 2260992	
2019-09-13T20:23:03+0200
Error	no app in context	Sabre\DAV\Exception\BadRequest: expected filesize 2279751 got 2260992	
2019-09-13T20:23:03+0200
Fatal	webdav	Sabre\DAV\Exception\BadRequest: expected filesize 3299481 got 409600	
2019-09-13T20:07:28+0200
Error	no app in context	Sabre\DAV\Exception\BadRequest: expected filesize 3299481 got 409600	
2019-09-13T20:07:28+0200
Fatal	webdav	Sabre\DAV\Exception\BadRequest: expected filesize 1024000 got 696320	
2019-09-13T12:09:09+0200
Error	no app in context	Sabre\DAV\Exception\BadRequest: expected filesize 1024000 got 696320	
2019-09-13T12:09:09+0200
Fatal	webdav	Sabre\DAV\Exception\BadRequest: expected filesize 4221465 got 212992	
2019-09-11T16:25:49+0200
Error	no app in context	Sabre\DAV\Exception\BadRequest: expected filesize 4221465 got 212992	
2019-09-11T16:25:49+0200
Fatal	webdav	OCP\Lock\LockedException: "Dateien/FORTU/Objekte/zz Objekte alt und erledigt O-Z gesp 190915" is locked	
2019-09-09T03:21:31+0200
Fatal	webdav	OCP\Lock\LockedException: "Dateien/FORTU/Objekte/zz Objekte alt und erledigt O-Z gesp 190915" is locked	
2019-09-08T02:19:38+0200
Fatal	webdav	OCP\Lock\LockedException: "Dateien/FORTU/Objekte/zz Objekte alt und erledigt O-Z gesp 190915" is locked	
2019-09-07T01:13:05+0200
Fatal	webdav	OCP\Lock\LockedException: "Dateien/FORTU/Objekte/zz Objekte alt und erledigt O-Z gesp 190915" is locked	
2019-09-05T23:19:08+0200
Fatal	webdav	OCP\Lock\LockedException: "Dateien/FORTU/Objekte/zz Objekte alt und erledigt O-Z gesp 190915" is locked	
2019-09-04T23:07:43+0200
Fatal	webdav	OCP\Lock\LockedException: "Dateien/FORTU/Objekte/zz Objekte alt und erledigt O-Z gesp 190915" is locked	
2019-09-03T21:30:06+0200
Fatal	webdav	Sabre\DAV\Exception\BadRequest: expected filesize 1788905 got 196608	
2019-09-03T11:28:38+0200
Error	no app in context	Sabre\DAV\Exception\BadRequest: expected filesize 1788905 got 196608	
2019-09-03T11:28:38+0200
Fatal	webdav	Sabre\DAV\Exception\BadRequest: expected filesize 2834987 got 1671168	
2019-09-03T11:24:07+0200
Error	no app in context	Sabre\DAV\Exception\BadRequest: expected filesize 2834987 got 1671168	
2019-09-03T11:24:07+0200
Fatal	webdav	OCP\Lock\LockedException: "Dateien/FORTU/Objekte/zz Objekte alt und erledigt O-Z gesp 190915" is locked

Have you looked at the activity log for the user logged in at the file server? It sounds like someone is deleting files.