The GPS Receiver does not need regular updates to keep it accurate. It is either working correctly or not. Have you changed anything on the boat, perhaps moved the GPS Receiver or added something that may now be blocking the satellite signals from getting to the GPS Receiver?
Go to the GPS Diagnostic View and let us know what the readings are for the Fix Type, HDOP and EPE (Estimated Position Error).
Have you always used that same Navionics map card or have you added it or changed to a newer one?
The only way to make things show “off” would be if the GPS Receiver is not tracking the satellites properly, if a new/different map card was used or if you somehow used the Map Offset function as LocDown stated.