The cause of this is a change made by Google in their “API call”. Adobe has made the required change so that Map will work in Lightroom Classic 8.0 and future versions, but they don’t go back to old versions of software to fix issues that arise.
Lightroom CC 2015 and Classic CC 7.x users: If your system specs meet the requirements, use the CC app to upgrade at no additional charge to Lightroom Classic CC 8.0 (or the most recent version if you’re reading this article after November).
Here’s a workaround for seeing GPS coordinates mapped, from Adobe: “To see the location of an image on a map, copy the coordinates from the GPS field in the Metadata panel located at the right in the Map module. Then, search for these coordinates on the Internet.”
Note that already-populated GPS latitude and longitude and location metadata fields (populated by reverse-geocoding / address-lookup or otherwise) on your photos will not be deleted.
Here’s a workaround for viewing photos on a map that have latitude and longitude (thank you to Laurie MacBride for suggesting this):
In the Metadata panel in the Library module, find the GPS field (in the dropdown at the top choose Default or Location). Alt/Opt-click on the arrow to the right of the field. This will launch your default web browser map (Google Maps, Bing, etc.) and will place a pin in the correct location.
For photos without latitude and longitude, out in Google Maps or another map program, find the location on the map and then copy and paste the lat/long information into Lightroom’s Metadata panel GPS field.
PS: Generally I support Adobe’s policy of not maintaining old versions of software, but usually when a new version comes out, the old one is no longer available for sale. I don’t agree with their decision to continue selling Lightroom 6 but not fix it when it breaks. (I do know the Lightroom product managers though, and I do believe that the decision was not made lightly and was not a plot to force you to upgrade.)