client crash report: https://pastebin.com/R70QSYDm
server crash report:
Issue: 1.12.2-r140 crashes dedicated server Forge 1.12.2 build 2760

Notes:
NoClassDefFoundError

crash report:
https://gist.github.com/51ddae5878ad9a94dee0f8e6b39e93fa

fml server latest:
https://gist.github.com/a892bd991bc2cd25cf07bc2b6114d67c

Uh wat. Are you sure that aa jar isnt corrupted?

How did you investigate it? Did you start a server instance in the IDE with it or did you put it on a true dedicated server? Need to know so I can compare your "investigation" method with mine.

I downloaded it straight from curseforge into my server with wget btw.