Forge: 1.12.2-2575
RC: RecurrentComplex-1.4.6

crash report:
crash-2017-12-26_15.52.15-server.txt

With the same version of Forge and RC.

I'm getting similar errors.

java.lang.Error
	at ivorius.reccomplex.commands.RCCommands.onServerStart(RCCommands.java:129)
	at ivorius.reccomplex.RecurrentComplex.onServerStart(RecurrentComplex.java:176)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

In fact removing Recurrent Complex bumps up my FPS by 10 or 15.

I think your VM settings may be off. Try increasing the space MC gets.