Ejector,
The gauges, which compensate for fuel temperature, are telling you the truth.
Full tanks implies a fixed Volume, and if those tanks are full of hot, low density fuel, the total fuel weight / mass will be lower. Conversly, if the tanks are full of cold, high density fuel, the total fuel weight / mass will be higher.
Important to note that all engines, be they Jet, Turbo-Prop, or Piston, require fuel mass, not volume, for their operation, thus Fuel Quantity Indication as Weight or Mass is far more valuable than Volume.
Regards,
Old Smokey