When I attempt a backup, it runs apparently to completion -- the log on the tablet screen ends with "Backup completed successfully", but the Companion app (on MacOS Tahoe 26.2 running on a  Mac Mini) reports "The backup has failed.  There may be problems with the tablet backing up the files or a connectivity problem".

Screenshot of the dialogue boxes reporting the error:
   

Is there anywhere I can look for a log file of the backup to look for additional error messages?