Crash at startup with these mods installed. I have tested it in a clean setup with the details below
MC 1.6.5
Forge 36.2.22
RoadRunner-mc1.16.5-1.4.0.jar
ImmersiveEngineering-1.16.5-5.0.7-143.jar
immersive_geology-1.0v5.jar
Crashlog: https://pastebin.com/QEvD4BJN

Looking into what I can do with fixing it

Can you elaborate precisely, how did you got this crash?

Getting the same crash on startup, Roadrunner installed.

@UnSchtalch This crash can be reproduced by simply using the mods stated. The game won't start and just straight up crash.

Also happens without RoadRunner. Not at startup, but e.g. when placing Uranium Sheetmetal Stairs from the creative menu: https://gist.github.com/malte0811/e05c6e757414e90536606638c4ed1eaf

Bump up the priority, I'll be looking into this further.

Also happens without RoadRunner. Not at startup, but e.g. when placing Uranium Sheetmetal Stairs from the creative menu: https://gist.github.com/malte0811/e05c6e757414e90536606638c4ed1eaf

Wait.
Uranium sheetmetal stairs. In IG 1.0v6?

Looks like we've broken datagen here, they should not exist, according to code.

I think you may be missing an override for hasStairs in MaterialMetalUranium. The hasPlate override stops the recipe from being generated, but the block still exists and is present in the creative menu.

Fixed and yeah, you were correct @malte0811, it was the missing override!