Minecraft Version: 1.11.2
Trace + info: https://pastebin.com/aCzefbuL
FML: MCP 9.38 Powered by Forge 13.20.1.2386 97 mods loaded, 97 mods active

I tried typing in "*stair(" -- I hit the brace by accident, and it thought there was a regex group in play.

Good luck with the fix, if you don't plan on updating the 11.2 version I'll have a go at fixing it if there's a branch to work off.

It may be worth noting I was able to get back on after the crash and remove the brace with no issue.