Simply, SG and SG:Extra Parts are 2 of the mods in pack that don't work on MC 1.12.2 (as you probably expected),

I'm surprised Forge updated so quickly. But this will probably be another effortless update for mods, like 1.12.1 was. Just need to update the version range.
Just so you're aware, the next build will likely be marked as an alpha. I'm adding new gems, so expect missing models/textures on some new blocks. Everything else should work as intended.

Ik. I'm up-to-date with the changes.