Had a similar problem with our 2016 35E Excursion. Fuel leaked from the hose connection to the tank on one side when tank was full and fast cutoff on other. Fuel hose is custom cut and installed by Fleetwood. Fleetwood said it was a Freightliner issue. Freightliner didn't have a part number for the hose so it was a Fleetwood problem. I ended up paying Freightliner to fix one side out of ignorance. Got Fleetwood to fix the other on the second go around. Its one of those grey areas between the chassis and the coach so if not fixed already you might need to reason with Fleetwood to get them to take ownership.
Hose on one side was cut too short causing the leak. Hose was cut too long on the other causing enough of a dip to pond fuel and cause early cut off. Once both those issues resolved fast fueling works fine either side but it is a shallow drop regardless and might need to slow fill the last few gallons.