I have found one bug. At active mod, event Old One's Army not spawn monsters. It is their spawn only when the player approaches closely the portal.
I've run in to this to, I'm wondering of the strange portals spawning with prefixes is causing it. Monsters will only spawn if the player is within ~5-10 blocks on the portal and despawn if the player moves away.
I've tested this in a fresh world with prefixes deactivated and the event worked fine suggesting that this mod is the cause.