I reported this in a modpack github originally:
Freebi85/Dungeons-Dragons-Space-Shuttles#113

If more info is needed, let me know. If you feel this is not related please close the issue.
Foamfix version: 0.10.3-1.12.2

Sounds like Galacticraft's emitting absolutely absurdly large textures into the atlas. It shouldn't be doing that, but FoamFix should have no effect on it either.