I think the GPS 12 may suffer from the 'Week roll-over problem', to check this you need to check the date displayed by your GPS 12, if it is more than 10 Years before or after the current date, you have a problem because it will never get a satellite fix. There is a fix for this but it involves downloading a computer program that sends a new date to your GPS 12
I have a GPS 38 that is about the same age as the GPS12, but you can't set the date on it so if it resets back to a pre 2000 date it never finds any satellites.
Units which get the date wrong after 6th April 2019, typically G95 types, can be corrected by the program released by Garmin 20 years ago but fixes the problem again: GpsEow.zip
Garmin supplied a Windows sensor configuration program called SNSRCFG_320.exe that can be used to change the date on these sensors which can fix the rollover problem: https://www8.garmin.com/support/download_details.jsp?id=925