⚠️ SMB (Samba) shares worked, now broken - macOS Monterey 12.3. What to do?

Up until recently, it was all working fine - copying files from my Mac M1 to my mini-NAS via Samba. I can still access all the files, but I can't longer save them to the NAS.

Now, every now and then, I randomly get "Finder wants to move XXX - Touch ID or enter your password to allow this."

When I do, I then get: "The operation can't be completed because you don't have permission to access some of the items."

Which items? What permissions? Why is this happening all of a sudden? 😱

I did not change anything on my end.

What can I do?

Thanks!