Hi,
Generators have a floating neutral.
You can correct it by adding a "bonding plug" on the generator.
The easiest way to do a N-G Bond is to create a N-G Bonded Edison Plug, this is done by simply buying a replacement male plug and wiring the Neutral (White Wire/Silver Screw) to the Ground (Green Wire/Green Screw) using a 12-14 Gauge piece of wire. Just make darn sure you don’t wire the Hot leg tot he ground. Then when you need to power something like a RV or HE Furnace with your generator you plug it into a empty outlet.