Interesting & informative. Good post.
I didn't know TM's drive must be formatted as HFS+, although I should have realized as my TM drive was formatted before (so, HFS+) I upgraded to High Sierra (and as my MBP 15 drive is SSD, it auto-converted to APFS). Moreover, I had not noticed any changes as to how TM was completing backups after my upgrade to High Sierra. Nonetheless, I'll keep this key detail in mind (I periodically erase / reformat my external, TM drive) until such time TM provides for backups to an APFS formatted drive.
Thanks for the link.
