On servers with Stacc installed (e.g. those that have Numismatic Overhaul), the cobblestone generators never stop generating cobblestone, even going past the max stack size (our server had it at 350K).

This is because the cobblestone generator code doesn't check the max stack size of the cobble, and just blindly increments it, thus relying on SimpleInventory#setStack to cap the max stack size, which caps it to the global max stack size. This is 64 in Vanilla Minecraft, but this is changed by Stacc to be the maximum stack size across the registry.