Not sure who can fix what in this situation so I left the information on both githubs.
https://pastebin.com/S2hvzdkK
Railcraft/Railcraft#1162

file.zip
try this one. (you have to extract the jar file)

I can't reproduce the crash.
Are you sure it's caused by railcraft?

Removing the newest version of railcraft allowed the pack to boot. I'm wondering if this has anything to do with JEI #28 since that was also updated. But the two together don't crash. Only when RC update was introduced.

Just re added the new version of RC in a local test build and crashed again. Removed it and replaced with previous version, loads just fine.

Didn't work. Covert Jaguar seems to have claimed its his mod and that it happens without Block Drops though I can not reproduce without the two being together. Sadly this means I might get a fix in 4-6 months :P Thanks for looking into it though!