Latest Affected Minecraft Version: 1.12.2
Latest Affected OTG Version: 1.12.2 v2

Some Forge terrain gen events aren't correctly fired by OTG during terrain generation. This currently breaks mods relying on these events. For example, OreGenEvent.GenerateMinable isn't fired with the GRANITE, ANDESITE, or DIORITE types. This breaks Quark's marble, limestone, and revamped stone generation.
The main culprit looks to be platforms/forge/src/main/java/com/pg85/otg/forge/events/OTGToForgeEventConverter.java. Some additional logic here should fix the issue.

Hey, thanks for reporting this, that's very helpful :). Fixed in 1.12.2 v3 / 1.11.2 v9 (release asap).