Playing 1.19.80.21. I've had this problem since 1.19.80.20 as well. I've found it happens after saving/quitting and then reopening a world. It seems like all villagers aren't recognizing their workstations as soon as the world loads. If I break the workstation connected to a villager and place it again and wait until it reconnects, the villager is able to gain experience again. As soon as I save/quit and reopen the world, all villagers default to not being able to gain experience again and I have to break/replace each villager's workstation to fix it. The experience level of each villager does seem to be preserved, though, so I can access trades from whatever level they were before saving/quitting/reopening, even if I don't break/replace the workstation. Also as soon as I break/replace the workstation the villager resumes at the level and experience amount it was prior to saving/quitting/reopening.
Playing 1.19.80.21. I've had this problem since 1.19.80.20 as well. I've found it happens after saving/quitting and then reopening a world. It seems like all villagers aren't recognizing their workstations as soon as the world loads. If I break the workstation connected to a villager and place it again and wait until it reconnects, the villager is able to gain experience again. As soon as I save/quit and reopen the world, all villagers default to not being able to gain experience again and I have to break/replace each villager's workstation to fix it. The experience level of each villager does seem to be preserved, though, so I can access trades from whatever level they were before saving/quitting/reopening, even if I don't break/replace the workstation. Also as soon as I break/replace the workstation the villager resumes at the level and experience amount it was prior to saving/quitting/reopening.