Restore an older version of GPS

I would delete all maps (i.e. all img files in the GARMIN folder) and reinstall them via Garmin Express. 

Out of curiosity: Which GPS version is now displayed after you downgraded to 15.20?

Now is GPS 5.50.

About delite all maps is it safe, is someone can me which exactly which files to delete, and is it unlock after that?

Same issue with my Fenix 6 Pro

Possible to share the old 15.20 version Please? I have the exact same issue.

This is list of file in my Garmin Fenix 6 pro in folder Garmin, can someone explain me what is this file, because cant solve problem with error "Cant unlock maps"

Here the map files are explained: shop.talkytoaster.me.uk/how-to-identify-and-or-remove-garmin-pre-installed-maps-on-a-fenix-etc

I do not think that the maps can influence the time the watch gets the GPS fix. You need fresh ephemeris data (the CPE file). Also, often, after a firmware update, a restart or a soft-reset of the watch is needed. For refreshing the CPE file, or fixing it if it is broken, you best delete it in the folder //GARMIN/REMOTESW and then check for updates with Garmin Express - that's the safest way to get a good CPE file.

What Is EPO or CPE on a Garmin Product? | Garmin Customer Support

Gluki already resolved the GPS issue. This is now about the "can't unlock maps" message.

Please try updating to the latest beta, v23.82, and comment in the beta bug reports if the issue persists.