I just tested the map after adding moongates at each core & core shard, and it seemed to all work properly. Not sure if this workshop item updated to the new version or not

I did an edited version with a tile and moongate added to each core, with a 2nd moongate in each portal area, but the computer AIs were overwhelming, even on Normal level. What seemed to work best was adding a Core Door to each core, and creating a path out of the rock surrounding each core. With no way out of the core at all, if you want to keep that feature, you'd probably want to ban Titans--since they can't leave an isolated core at all.
As I mentioned in a comment yesterday, I tried placing one worker in each portal area as well, but the AIs eventually just recalled them --even when I left a plain dirt tile leading out of each area.

Thanks for the info & sorry for the late reply! So you're saying that I should add the moongate constructs for each player? I didn't think of that the bots wouldn't pick up to move the imps/workers around.

Moongates did not work--game went by way too fast, I tried putting one worker in the core shard/portal area, other players still did not respond. I ended up putting in core doors and a path out for each core, and two of the other players responded, with play on medium

I quit the game, reloaded, found the map, may make some edits myself.

I played through to a finish with all other underlords on normal, then restarted with them on master level. At no time did the other players build anything. The workers never left their cores. I would suggest putting a moongate at each core, and another near the gateway. I was going to try this myself, but could not find the map in the map editor list. I did claim the nearby nether shrine, but the banshees did not enter a moongate to reach other moongates, but simply destroyed my own area.