I'd try removing RP2 from the server, then loading the game up again. If that doesn't work, move one by one through all the mods that have world gen. If that also doesn't work, try all the ones whose blocks you used on the tunnel bore. After that, just do the rest of them, I suppose. If it starts working again, you should be able to add all the mods back in.
Important Note: Taking a mod out and loading up the world will remove all blocks and items from that mod permanently. This includes world gen and blocks you have placed, as well as items in your inventory (and possibly in chests). You should only do this as a last resort, which it looks like you're up to right now.
