New build: http://files.player.to/fastcraft-1.23.jar
It should fix compatibility with ruinsmod and named entities with invalid AABBs used for serverside banners. Turning off enableCullingTweaks doesn't crash anymore.
If you feel comfortable with it, mind pushing it to stable? Mod pack devs I am talking to say they will add it however it needs to be stable. They want to push the updates tmr/wed however will only add FC if its set to rec/stable.