Time Machine failed, smb error stat_ex.st_ex_blocks differs

On my brand new mac mini (big Sur with M1 architecture), a big multi terabyte timemachine job failed after a day or so during 26 Nov evening but I wasn't there to see the message.

At the Apple end you just get a generic error saying the backup failed with no details.

I've grabbed the complete /var/logs directory for you (see attachment) in case it's useful.