Two issues today.

1. Unable to check in via OP# or Conf# - eticket # worked. Message stated that there were no flights eligible for check in when I tried with the OP #, and no valid itineraries eligible for check in when I tried with the confirmation number. The e-ticket # worked, but by then I was #8 .
2. I checked the seat assignment (14a) didn't change it, hit continue and ended up in 28B (IIRC). Quickly fixed (no harm done), but it seemed odd. I'm pretty sure I didn't click anything but "contiinue" on the seat selection screen.

Update: Couldn't get in again today with OP or Conf. Called co.com support. They checked and explained that this occurs when EUA is running (not in those words). I assume that they lock records. Note to CO.COM IT: have you heard of read-locks?