We discussed this crash on discord a few weeks ago. I thought I had reported it but I realized I must have forgotten to click the submit button.

This is the crash log from my game : https://mclo.gs/ik1vAt3
Crash log of MildlyMiffed#6394 https://mclo.gs/Tt6nIqs
Crash log of rose_#7017 https://mclo.gs/xlDn3aC

Since the discussion on the discord, I have published the mod pack
I was working on, If you want to try and recreate it yourself, try and add environmental to it:
https://www.curseforge.com/minecraft/modpacks/bumblemancy

I'm pretty sure I'm hitting this as well with a modpack I'm working on. Just a solid hang a little after Dispatching Module Step CONSTRUCT_CLIENT shows up in the logs.

Same thing seems to be happening to my friends but not me with the same set of mods. Ceases shortly after Dispatching Module Step CONSTRUCT_CLIENT
Log:
environmentalhanglog.log

Since this is all one issue going to redirect this to #362