The game starts a lock up and you can't move much so the game becomes unplayable if you have the Aether II mod installed...

Versions

Betweenlands version:

Won't matter. I have tryed a few.

Forge version:

1.12.2

Singleplayer or Multiplayer:

Happens in both single and multiplayer.

Description of the problem

How to reproduce:

Just install this mod with any other mod that adds Dimensions like the Aether for example.

I can't reproduce this. Perhaps your game is running out of memory, see https://cubedhost.com/help/en/articles/1648388-how-do-i-allocate-more-memory-to-my-minecraft-launcher-client-side