MC version: 1.15.2
Forge version: 31.1.75
Crash log:
2020-05-06-6.log
Happens in "FML early loading" stage.

debug.log
modlist.txt

Remove tpsgenerator-1.0.jar, The mods manifest contains a MixinConfigs entry but there doesn't appear to be any Mixin related stuff in the mod. The entry was probably added during development but then never removed.

@Tfarcenim - mentioning the developer here as this mod doesn't have an issue tracker on CurseForge or GitHub.

Please provide the debug.log file as well as the list of mods you have present so we can track down the mod which owns tpsgenerator.mixins.json

Removing that mod solved the problem. I've informed the developer at CurseForge.

I am having the exact same issue but with only the latest Forge, Mixin and Optifine (15.2) and nothing else running.

It crashes without generating any log files even.

Disabling MixinBoostrap completely solves the problem.

I tried a fresh minecraft with nothing but MixinBootstrap and the current forge. No dice.

Please provided the debug.log file

There was no debug.log. I can't see any such file anywhere anyway.

However I solved it.
If I manually install forge in .minecraft and run it with mixin it works fine.

The issue only occurs when I setup a modpack in twitch.
I was able to copy the complete profile into a twitch directory and load it in twitch and it runs fine now.