When the game begins pre-initialization, it will crash as soon as it reaches Patchouli. This is due to Patchouli throwing a NullPointerException, as showcased in this hastebin: https://hastebin.com/usunodipeq.rb

Patchouli is version 1.0-16
forge-1.12.2-14.23.5.2811

I had a similar issue, caused by me not specifying "version" in book.json, I manually set it to "0" (which should be the default according to the docs).