I get a large number of entries like this in the log file:

[01:26:56] [Server thread/WARN] [FML]: MalisisCore loaded a new chunk (-15, -27 Dimension: 0) during chunk population, causing cascading worldgen lag. Please report this to the mod's issue tracker. This log can be disabled in the Forge config.

Malisis core: 1.12.2-6.4.0
Malisis doors: 1.123.2-7.3.0
Forge 1.12.2-14.23.2.2611

and a large number of other mods.

It's a wrong report. MalisisCore don't do any worldgen, it's just Forge trying to guess what mod causes it and failing.