Ground fault only when running generator

I have a multiplus II, Cerbo GX, GX50 & smart solar setup.
All works fine, except when I charge batteries with my Honda EM 6500sx generator. The generator charges the batteries fine, but if I plug in one of those plug testers, it shows an open ground fault at every a/c outlet in the house. The outlets all still work. If I turn off the generator, the fault goes away. If I run the generator not wired to the house, no fault on it either. It only faults when generator is connected to the victron breaker box . The generator says it is a floating neutral generator, which I have confirmed by testing for continuity between the neutral and ground with generator off. (no continuity, so not bonded). The multiplus appears to be internally bonded, since there is continuity in the victron box between the neutral and ground bus bars. So my understanding is that the generator should look to the victron system for the bond, and all should be good, but it isn’t. A friend said the multiplus has some sorta switch for changing the automatic internal bonding. Where? Suggestions?

The muliplus should have a programmable ground relais

Perhaps look at a neutral earth link in the generator.
You can also set the multiplus to do that for you but the best way is to make the generator output without a floating earth

In normal operation via AC In … whether generator or mains … the Multi opens its ‘earthing relay’ because it assumes that a ‘neutral point’ is established between N and PE at the power source. For generators that do not have this, this must of course be activated permanently at a later date or this bridge must be made ‘manually’ on the generator as a permanent solution.