This actually is a bug and happened to me as well. Had fare locked a Dca- Ewr reservation and went to purchase it on day 5 and as soon as I clicked it, it straight away said the reservation doesn’t exist or was canceled. Called UA immediately and they told me that I had canceled it. I was dumbfounded and just plainly told them that the link I clicked was the purchase reservation, not cancel. The fare had gone up by $80 in the 5 days since I had blocked it. The CS rep had to get the fare desk to reprice it and regenerate the fare and have them give it to me. Even then it wouldn’t ticket. Had to call again and get a supervisor to ticket it.

so it’s a bug happening to multiple people or so it seems.