Can you see your water tank to see if it is actually a third or full? Sensors are typically bad and if you have the all in one control panel and monitor like in my 2017 Flagstaff they have more gauge issues then most. I believe there is a recall for these panels.
I am not sure how you are determining hot water flow if the cold is on. please clarify what you are doing. in general check the water heater bypass valves, should be 2 or 3. and be sure the outside shower is off.
TT 2017 Flagstaff 831CLBSS Classic Ultra lite
TV 2017 F150 6.5' bed 3.5 Eco-boost
prior TV 2014 Silverado 2500 HD