Hmm then this might not work in your case. I've never used mekanism so idk what sort of incompatibilities there may be with GT, GC, and mekanism. The issue does lie in the forge fluid list. You could try generating worlds with and without GT or GC or mekanism and see if subbing those fluid lists in fixes the issue. Idk these are just shots in the dark.
If I'm not wrong, my previous world did not have Mekanism in it and it was perfectly fine. I guess I'll look into the issue with Mekanism and the forge fluid list.