Try Restore Defaults under the Setup tab ...
If that doesn't help it's possible you may have a corrupt waypoint creating Gremlins ...
You can export your waypoints and open them in Humminbird PC (which is available in your HB account on the HB website) ... In Humminbird PC look for dates that don't make sense or duplicates of longitude and latitude...
Once your waypoints are safe in Humminbird PC - Format Nav Directories under the Setup tab / Restore Defaults again and test the unit operation on the water ...
Rickie