All Vortex boats have a GPS-based speedometer, and many of the boat’s functions are based on a good GPS signal. After a certain time, for reasons undetermined, the Medallion can lose “sync” of GPS satellites. You will notice this is your speed readout is obviously way wrong, the cruise control functions won’t work, and your maps are way off.
The usual solution for this is simply to turn off your engines in a safe location, then turn off the main power switch at the battery for 30 seconds, allowing the Medallion to fully reset. Turn the switch back to On, start your engines, and proceed.
Almost every time your GPS speed and other functions will be restores, after a GPS lock is achieved. (Note, after reset it may take a couple minutes to get a GPS lock.)