This is probably the best place to ask. I’ve never heard of this issue before. I did some googlefu to check up on what other people have said about this.
The “extension unit” unit won’t solve your problem. Most people don’t understand what this was. It’s just a piece that caps off the extension slot on the Genesis. It literally does nothing. Only first run 32X units even included it. Sega threw it in to get FCC approval. The FCC later approved 32X to work without the dongle, so units stopped coming with it. It literally does nothing.
My first instinct would be that there’s something wrong with the actual board in the game. It never hurts to take apart the cart and see if there’s water damage or if it needs to be cleaned on the inside.
Because other people are having problem with the same game, maybe there’s also a problem with a certain batch of this game.
The other predominant theory out there is that the game has an incompatibility with certain revisions of the Genesis 2 motherboard. I’d suspect the VA2 or VA2.3 revisions, as they have completely different video encoders than most Model 2 units. Or, it could be that you have the rare Majesco version of the Model 2.