I had this happen to me about 6 weeks ago. I wasn't showing on the upgrade list for my connection upon landed, so I called the PM line and she said it looked like I had removed myself or that there was something else wrong. She tried to fix it but it was already under gate control.

By the time I made it to the gate they were ready to close the boarding door, so I by far missed the upgrade even if I could have gotten the GA to put me back on the list.