Killing Wandering Trader and his Llamas prevent the game from saving correctly

What actually happened was...:
1.A Wandering Trader spawned near me with his two Llamas naturally ,then I killed the Wandering Trader,but what surprised me was that the Llamas behaved like stones after I killed the Wandering Trader,and the Lead on his hands didn't turn into an item that I could pick it up.After that,I tried to quit the game,but it stopped at the screen of "saving the world...".The game was finally not be saved.

2.I reopened the game,and killed the Llamas first.And then,I killed the Wandering Trader.The game continued,which seemed that nothing happened.I tried to quit the game at this time,but it still stopped at the screen of "saving the world...".The game was also not be saved.So,if I killed them,my game would not be saved correctly.