Hi! I play in 1.12.2 and the ores do spawn, but it's weirdly rare. I haven't made any changes in the config files of neither of my mods (this, Base Metals and Modern Metals)
Modern Metals are spawning more than Base, but it is minimal the amount of ore, I have to use X-Ray mod to find them.
Could it be an incompability with CoFH World? If so, is there a way to change the ore generation from MMD to CoFH?

I've got almost no experience with CoFHWorld, but yes - there is an option to turn off the need for OreSpawn in the "Metals" family of mods and you can add the spawns to the world using CoFHWorld.