Description of the Bug
If you spawn an invalid block (in this case its Galacticraft) such as galacticraftcore:basic_block_core into your inventory the game will crash, this does not happen without railcraft.

Without Railcraft

With Railcraft

• Full log:
  Unable to upload, for whatever reason.
• Crash report (If available):
  https://paste.dimdev.org/uzubozavef.mccrash

Hmm, how can there be a -3 meta? need to ask galaticcraft dev.

I spawned it in by accident, that's how I found this issue :P I think it's possible to spawn invalid items with any mod, but I will connect this issue with a Galacticraft issue.
Appreciate the speedy response btw

Seems like the galacticraft team fixed the issue on their end, its up to you if you want to close this.