In retrospect, I worded it a bit stupidly. I meant that he just stands by the bookshelf all the time and refuses to take on any job. We checked the trading hall and the surrounding area in survival mode (and in a copy world in spectator) and didn't find any other lecterns, except for the ones for the villagers in their 1x1 box. When we placed a new lectern next to him, he never reacted (no green particles) but all other villagers with other jobs were able to target their blocks again.
Well, I have this bug too. Not once, not twice, but three times.
First of all, I have to mention that my world is already 2 years old and I play there with a lot of friends. Since this is my world, only I have OP rights, but since I have collected all the achievements with this world (and still want to), cheats are deactivated.
2 years ago I defeated the ender dragon with a friend and collected the first ender dragon egg, which went into the ender chest shortly afterwards.
About 8 months ago, 2 other players fought the Ender Dragon and then had an Ender Dragon egg. Since they knew that I had the first one, they reported it to me and after a conversation, they entrusted me with the egg. This also went into the ender chest.
About 3 months ago 2 other players had the same scenario. After a conversation, they gave me the ender dragon egg and I stored it (once again) in the ender chest.
And today I found the 4th ender dragon egg: I was on the way with a delivery of blocks to another player, who was building a map art in the End. On the way back I saw in flight that something was on the end fountain and when I approached it I couldn't believe my eyes because there was another ender dragon egg there.
But this time it was a little different. There was no ender dragon fight because the number of end transit portals exactly matched the amount stated in the last fight (which was the fight where we got the third ender dragon egg) and also none of the players reported having a fight against the Enderdragon again.
After this event, I created a copy of the world, increased the number to 30 with /setmaxplayers and invited every player and we discussed this bug in the voice call. I explained the situation to them first, because apart from the 4 players who received the 2nd and 3rd Ender Dragon Eggs and the 2 players who were present at the session for the 4th Ender Dragon Egg, no one knew that we had several Ender Dragon Eggs own. And as expected, none of the players had started a fight in the last 3 months and none had really had an explanation as to how this came about.
So I now have an extreme version of this bug, where the ender dragon egg has reappeared three times.
It lagged for me when i parked it at a wooden crane xD