I was fighting the new boss (twins of terror) with my friend, after we both died I rolled back to the previous save, but the boss did not dissappear. Not only did it stayed during daytime, it also caused an unexpected error(see the image below). It suggests that the error might be caused by the mods I used; I turned of all the client mods, and the same error still occured. I wanted to turn off all the server mods as well but I did not want to risk losing the save.
Any ideas on how to fix this?
summon the twins of terror at night, roll back to the previous day, and the boss would stay.