I have successfully configured my server with Forge version 1.12.2-184.108.40.20638, and everything appears to be working with the 80 mods I have uploaded, except that the World generation appears to be completely Vanilla.
I have tried editing the server.properties file to set level-type to "BIOMESOP", but I am not getting Biomes O Plenty biomes when I generate a new world.
I also cannot see any Tinkers Construct slime islands, and I don't believe the ore generation includes Thermal Foundation ores, Chisel marble, or any other modded content.
I also tried creating a new world using the Nitrado "World Manager" tool, but this does not seem to fix the problem.
I noticed in the Nitrado "File Browser" that several mods appear to be "greyed out". These include the mods for which World Generation does not appear to be working. I have attached an image showing that.
The craftable items for these mods do exist in JEI, it's just the world generation which appears to be borked.
Would appreciate any help! I tested this custom modpack on single player and it was working fine.