Just used a few hours to remove one mod at a time in a large modpack to figure out which one caused the issues i have.
It seems like its GregTech that does it.
Using minecraft.curseforge.com/projects/angry-pixel-the-betweenlands-mod together with GregTech, makes the dimension not load.
Using it just with IC2, GT and Between The Lands, makes the dimension not load.
When using the talisman on a oak sapling, then use the portal in the tree that spawns, makes the screen stay at "Downloading Terrain".
Removing GregTech 5U, makes the dimension loads again.
The bug can be reproduced with just:
TheBetweenlands-1.0.3-alpha-universal
gregtech-5.09.21
industrialcraft-2-2.2.821-experimental
This bug has also been reported to the dev of Between The Lands