UA has always been bad when it comes to maintenance disruptions, certainly in comparison to their direct competitor Delta. High load factors are making re-bookings more difficult these days which causes further inconvenience for pax. This week I misconnected at IAD and got home 5 hours late (yep, UA's fault) and had to call in from the arriving plane before we hit the gate to get the last seat on the last flight of the day ... else I would have been stuck overnight at IAD.
While waiting at IAD I saw 3 TATL flights with major delays; each of them due to 'maintenance'.
I have seen worse issues a few years ago, but it is creeping up again as far as I can see.