I think so.

I've reported this happening to me several times the last few weeks in another recent thread. Some other FlyerTalkers chimed in with similar reports as well.

Seat assignments are disappearing (Seat: n/a) for no noticeable reason. No time change, no flight number change, no equipment change. Even Reservations agents are puzzled.

So far, I haven't had any problems getting my original (or better) seats back. That's probably because I caught it right away and perhaps everyone else on those flights lost theirs too and hence seat assignment availability was wide open!

So yes...good idea to double check those seat assignments.