I had this problem even a few days ago on 1.16.1, but now, still, on 1.16.200, some villager trades are stuck locked. I've traded with one, the trade got capped out, and I expected to wait a few minutes until I could trade it again. It has been many many in-game hours, and the trade is still locked. It's been a few real days. I haven't heard of anyone else having this problem, but I am certainly having it.
To clarify, I'm playing on a bedrock realm. And to be specific on what's happening... I traded an Armorer. I maxed out his 4 iron for 1 emerald. The X is there and has not gone away.
Does the villager have access to its workstation block?