I hope I don't jinx it, but with 10.12.3 (and possibly earlier versions as well, I don't recall) my TM backups to external devices (rMBP to a Time Machine service on my nMP saving to TB RAID, nMP also backing up to TB RAID) would stop running at regular intervals after 1-2 scheduled backups but would run fine if I manually triggered them. It was frequent enough that I created a crob job to do a tmutil disable/enable every 6 hours to kickstart the backups again. Well, I'm happy to say that ever since the 10.12.4 update 3 days ago my TM backups on both machines have been happening regularly on their own again. With 10.12.3 neither of them would do hourly backups on their own for an entire day, so to have 3 days of regular backups is a miracle. Hooray!