I have exactly the same problem on Lightroom 6
Is your Develop module working? The reason I ask is, if your trial expires or your subscription becomes inactive, both the Maps module and Develop module will become unavailable for use until you update your subscription.
This doesn't seem to explain retainer's problem with LR 6 though.
I upgraded to LR6 from LR5. So it is not the trial version and everything else is working ok.
Apparently Google does not allow some countries to use the map module. I don't know why, doesn't make any sense to me.
In LR5 there was a menu under "Help - Lightroom Registration" where you could change the country. In LR6 there is no such menu.
This thread has a response from an Adobe employee: How can use map option to be able to geotag my pictures in lightroom in Istanbul - Turkey region ?
Due to legal restrictions Google places on our use of Google Maps within Lightroom, we are not allowed to enable the Map Module in Turkey. (We know your region based on what you enter under Help -> Lightroom Registration...)