While Mod tries to generate their structures it sends to console warn "Worldgen cascading constructions"

Also many times i see such constructions in world.
Weird construction generation

Sometimes if i loaded new chunks with my friend it causes a crash of server.
My crash report

Server memory 1-2gb
Forge 14.23.0.2491
Reccurent Complex 1.4.5.1
Minecraft 1.12.2

For the cascading chunk problem, see #155. It's a bug, but it's not critical for anything.

I don't recognize the structure. Could you go inside and run /#whatisthis? It's possible it was just saved as-is (with the strong borders).

The crash report is a java error - so a problem with the java distribution itself. Try updating your JVM. It really shouldn't occur often though. If it does, please open a new issue for it.