I use a bonding plug with my champion 2000 watt inverter generators. When I'm paralleling them I only have to have the jumper plug on one of the generators.
As mentioned the jumper plug probably isn't your problem. The surge guards are more sensitive to low voltage than the protection circuits on the generator. My Progressive EMS trips immediately at 104VAC whether it is in bypass or not. With my 15k air conditioning units I can't reliably run the ac with the little champions paralleled without the EMS tripping. With my 3500 watt HF inverter generator, I can start them reliably only if I don't use the ECO setting on the generator. The hotter it is, the more power your ac uses at startup, and the higher your elevation the less power your generator puts out both of which can cause issues. I have a couple hard start caps I plan to put on my dometics at some point but haven't gotten around to it yet. Too hot on the roof right now.
Good luck, and let us know what you find
