The Saturn cartridge slot can be very temperamental. The things I would try, in this order:
Push the cartridge in all the way and then back it out just 1mm and see if that makes better contact
Put a thin card behind the cartridge so it is pushed forward just slightly and see if that makes better contact
Disassemble the console and use some contact cleaner on the slot. Be careful not to bend the pins.
Loosen the screws that hold in the connector just slightly
When you find the right position to get a cart working, it’s best to leave it inserted. This is why many people use the multi-functions carts, so that they don’t have to constantly swap carts and go through the process of trying to get a good contact every time.