Minecraft 1.12.2
Forge 14.23.1.2555
Simple Gravel Ores 1.8
JEI 4.8.5.135

Modded Ores don't show up in JEI, but they generate in the world.

Please explain your issue better. What do you mean by "modded ores"? You mean like copper, aluminum, etc? If so, do those ores exist elsewhere in your pack?

Yes, I mean copper, aluminium, lead. I have Immersive Engineering installed, so they are definitly in the pack.

I cannot reproduce in my pack. It should be impossible for that to happen since they either generate or they are hidden from creative/JEI

@angelnc1989 do you have unidict installed? I've heard it hides blocks with the same oredictionary name from the oredict, and my ore blocks are oredicted like the related ores.

That might be it.