Villager traded with but doesnt lock, but locks randomly after moving lectern. on another trade.

I am playing on a realm I own. Alone on the server. Long story short trying to set a villager trading hall basically, I got mending surprisingly fast I was happy and excited.

I went got some emeralds to trade with it to lock it in. I did and got my mending book and he got xp. Then I decided to redecorate and move his lectern. I broke it and he turned back into a normal villager, I placed it back and he returned to a librarian, different trades though. I broke it and replaced it again, but trades werent changing.

So basically bro just trolled me gave me hope then took away my mending and locked on some trash trades. No I did not trade after he lost mending he just locked by himself and i still had my mending book even and he still had his progress xp from me trading for the mending book. But then he changed and now hes useless and my day is ruined.