New backup runs into BackupHandler-FatalError

Hi

After a crash of my windows I cleaned and updated everything (corrupt system files). So far so good.
Now duplicati got serveral errors on the existing backups, which I think are from the crash.

So I started all over and did a completely new backup. But as well this backup runs in a Fatal-Error - reproducable.

[Error-Duplicati.Library.Main.Operation.BackupHandler-FatalError]: Fatal error\r\nUserInformationException: Failed to write to file, difference between bytes read and bytes written"

Question: what the hell can be wrong, that duplicati gets this error?

The Source is a checked local volume and the destination is an SMB connected NAS over Ethernet.

Could you give me a hint, what causes this error and how could I get a clean backup.

Thanks a lot!

kind regards