Certain files cannot be uploaded - transfer stopped with error 500

Nextcloud 11.0.0. installed through Softaculous app installer on commercial Nextcloud provider server, configured with max upload size 4 GB, PHP, Goodsync as synchronisation client.
Certain files can never be uploaded, not with Goodync, not via browser. 2 files about 650 MB, 1 file 560 MB, 1 file 990 MB size. In Goodsync file transfer stops after e.g. 80% upload or more and error message: error copying file: Server says: Internal Server Error (status code 500). And they are the same files which cannot be uploaded via Goodsync and via browser. I thought about trying Nextcloud client, but it apparently started to transfer all about 35 GB again, so I sticked with Goodsync.

I have had the same type of problem with the Owncloud installation on the same server earlier and could never get working support from the provider or Goodsync.

The same files can be uploaded e.g. to the cloud Mega.

Any idea here what I can do?