This look like a lots like this #73 Did you do the same manipulation with minecraft map ?

Can confirm. It sometimes creates the deformatted map right after generating it. Without need of placing it and destroying like in #73.

Does this happen all the time ? I tried to replicate this bug but i didn't manage to. Can you put the full command line you used (link included if possible) ? Just to make sure you are on 1.15.2 on spigot or paper? and you are using IoM 4.0pre2?