Description of the issue:

When loading the game with Immersive Engineering .84 and Gaspunk, the game crashes around the post-initialized stage of loading. I have reported the issue to the Gaspunk git as well, and they said the crash was likely on ImmEng's end. Removing either Gaspunk or Immersive from the game resolves the crash. Immersive .83 and earlier did not have this crash.

Crashlog:

https://pastebin.com/8u3BR4Qi

Versions & Modlist

Immersive Engineering .84
Gaspunk 1.4.5
Ladylib 2.0 (Gaspunk dependency)
Forge .2732

Looks to me like they ship an old version of IE's api. They should probably stop doing that.

Report to them.

Actually, the cause was something else entirely. I had an ore brewing recipe, without providing the ingredient in my mod. This doesn't cause any issue usually, but it results in an empty list of itemstacks when no mod adding items to that ore entry are present. Immersive Engineering doesn't handle empty lists, resulting in this crash. I fixed it by adding a condition on the recipe, but you may want to add some safeguards.