Backup didn't complete, but Watchman Monitoring caught it
Allen,
Watchman notified me that my Time Machine Backup had not been completed in 28 days. I was certain I had backed it up within the last week or two. I had plugged my mac in before bed and let TM run. The assumption was that time machine had successfully completed the back up. Thanks to watchman, I became aware that for whatever reason (TBD) the backup was not successfully completed.
Thanks WM
Barry