Backup catalog fails on NAS, not on local drive (v15.1.1 / MacOS)

Interesting problem:

MacOs 26.2, LRC 15.1.1

Backup catalog fails if I assign it to a network-NAS-volume. 

All my photos are on the same NAS-volume and I can read/write without any problem.

If I change the backup-location to the internal drive, no problem. Don’t want that, because the LR-catalog itself is on the same drive.

I noticed the backup process starting with much enthusiasm, then at about 40% it slows down, but does proceed till the end (compress). And then it gives up with an error message and tells me to check the rights and space (both fine).

I recently upgraded LRC from v12 (on older macbook, no upgrade possible due to old MacOS) to this version (on new macbook). The old setup did work with the same NAS without any problem (other than very slow). I did not try a backup v12 on the new macbook.

Working around now, backup to the same local internal drive as the catalog itself and copy the backup by hand to the NAS. 

Anyone has a clue? Thanks for your response!

Ernst