Thanks for that link. Very interesting! My wife has Sierra on her MBP (my MBP is too old to upgrade) and she is constantly getting backup error messages, most often the one where the sparse bundle can't be verified and you have to start over. Yesterday got a message that the backup could not be completed and to use Disk Utility to verify and repair the drive or just wait and it may work fine at the next backup (sort of a strange message, lol). I'm on El Capitan and have no problem at all with TM backups. My wife does not use the Storage Optimization mentioned in the article and he does think that the variable backup schedule only happens when Storage Optimization is turned on.