Body scan formulas are based on the assumption that your muscles are filled with glycogen (water), and since fasting reduces insulin, which is responsible for helping the body retain water, you’re not going to get an accurate picture of your muscle mass via scan while you’re fasting.
As far as I know, the only 100% accurate way to determine body fat and lean mass levels is autopsy.
Just go forward knowing that scans are not designed for fasting people and let your strength levels tell you whether or not you’re losing muscle.