Generating new chunks while holding a map causes game logic to run extremely slowly or even worse, stop at all.
The affected things are: chunks not being generated and you an fall in the void (without dying), Ice not generating from frost boots, not being able to get off the boat etc.
Most of this goes back to normal once you unselect map slot.

This is extremely annoying since i tried to rejoin the world for all this to get fixed, but instead i ended up in the middle of the ocean without a boat surrounded by drowns (happened twice).

This is how it looks like when the games just gives up loading anything: