Yes, I see this often. I've monitored the output of 'tmutil status' during a backup. A lot of what I see doesn't make sense. Time Machine prefs will show "Backed up ***.XX GB", but the backup continues going for hours with 'tmutil status' showing that the backup is more than 100% done. Sometimes I see 'files' and 'totalFiles' increase without an increase in 'bytes'. I'm trying to find out what those 'tmutil status' values are supposed to be. I have a 2020 Macbook Air and have only been able to back it up to an attached hard drive. For 3 months I've tried to complete a backup over the network. I haven't succeeded yet, even while hard-wired to the router.