I noticed 2 occasions so far when Combat Assist doesn’t re-engage after a certain event.
1) The first was during the quest ‘Ending as One’, where you must defeat two drifting Ea to lure out the unified Ea. When you kill the 2nd enemy and the unified Ea appears, Miqo will not engage it, thinks the battle is finished.
2) In Smileton during the last boss I died, and Miqo thought the battle was over. Would not re-engage. I died again, trying to recover manually, and was rezzed again with the same problem. It appears as if when I took the rez it thought I was in a cutscene.
Log from that battle shows:
(9:12:52 AM) Assist: ON
(9:13:56 AM) Battle: I am dead.
(9:13:56 AM) Battle FINALIZED.
(9:13:56 AM) Oops I died.
(9:14:05 AM) Watching cutscenes :3
(9:14:07 AM) Oops I died.