Creating a world won't work. Your simply stuck in the Loading world, building terrain stage of world creation.
The logs are simply spammed with

[20:56:15] [Server thread/WARN]: Recurrent Complex loaded a new chunk [-54, 32] in dimension 0 (overworld) while populating chunk [-55, 33], causing cascading worldgen lag.
[20:56:15] [Server thread/WARN]: Please report this to the mod's issue tracker. This log can be disabled in the Forge config.

The logs say to report this to here and well, that's what I'm doing. Without this mod, a world loads just fine. So, its this mod.

same issue, whenever I put something in active world generation freezes or when I /#gen anything from inactive nothing appears, slash commands no longer work and quiting the world freezes.

in both cases I end up having to kill the game.

EDIT:
apparently it was a corrupted structure file, I've done some reexporting and it's worked great