This one is not feeling right to me. I know I said that I think it will probably sort itself out, but as you are still a long way from the flight date and have time to make sure it's squared away, I would do that.

I would call COPA again (painful, I know) and ask them again what they are seeing. If you get the same response that you are in Y waiting an upgrade, I would go back to UA, ask for the *A desk and not hang up until they talk to COPA and get you a seat assignment. Then, I would go back on the COPA site and double check that it took.