Some file garbled after sync with Win client 3.0.0

Garbled files

After client upgrade some local files got garbled.

Nextcloud version : 13.0.2, client 3.0.0
Operating system and version : Windows 7
Apache or nginx version : Apache 2.2.22
PHP version : 5.0.31

This particular issue is related to Server 13.0.2 and Windows client 3.0.0

After I upgraded Windows client to 3.0 (from 2.x) I noticed some strange behaviour: in some folders it started to generated strange .~ files. Then I added a new sync in a new folder.

The update went pretty ok except some files reported ‘internal server error 500’.
At next sync those files were synced sucessfully. At least from the SW point of view.
BUT, those files became garbled (e.g. some PDFs are not readable anymore).
The files have the same size and at first view no visible difference (text file).

No idea how to replicate it.

This is an old server(being upgraded multiple times since owncloud base) that has a planned full reinstall (OS + SW).
I’m aware that the server side is way out support.
Just wanted to warn if anyone is interested in debugging the client side.
I will keep the garbled files for a while.

Add on: it seems all garbled files have attached same begining of file.
see screenshot

The overwritten part is always the same (maybe except some id)