Previews don´t show on NAS

I have the problem that when I save Acorn files on an smb server, no thumbnails can be seen. If I copy the files to the Mac, the preview can be seen.
I work with Acorn 6, last update, from the App Store. The test version of Arcor 7 has also brought no change.
I have already deleted cashe and preference files, all without change.
Thanks greetings

I’m guessing this is because the NAS you’re using doesn’t have the type of disk integrity that is needed for SQLite documents to be opened (Acorn’s file format is actually a SQLite database).

Can you even open the files from the NAS?

Thank you!

Yes I can.

It is a Synology.