Now first, that’s something completely beyond Amanda’s scope.
Second, there’s issues related to CIFS such as those raised here.
I’m just guessing since you didn’t explain - it looks like you have a REALLY weird setup:
Server (your NAS) is a UNIX box, client (openhabian) is UNIX, but you’re using CIFS (Windoze !!) to share the disk ? What a nonsense. Move over to use NFS and you should be fine.