Hello,
Did some testing with server side:

1. Compile branch liach-1.12.2
2. Install clean forge-1.12.2-14.23.3.2691
3. Put Railcraft_1.12.2-10.3.1-unofficial-dev.jar to mods folder
4. Run server
   Crashed with: NoClassDefFoundError: Lmods/railcraft/common/util/effects/IEffectManager

Thanks for attention...

1. dev jar is not for mod usages. it is for modders to add as a dependency.
   2.the normal jar would crash to stop illegal distributions.

if you need more help, ask me on discord.