I wonder if this is just a Google Maps issue. It looks like the Lightroom end of things is working (for me). Perhaps the maps service that Lightroom uses is going through more changes than just the (I presume API-related) one that caused the offline error. Not sure...
I am seeing the "no imagery available" issue too. First noticed it yesterday (30 July), with random squares of the map being greyed out, depending on the level of zoom. In some cases, entire countries can be obliterated.
In addition, other areas of the map may appear as very low resolution (see the area below the grey square in the second image).
I am still having map problems after the July 2017 update. Now when I zoom in on the map, blank grey boxes appear on the map, sometimes with "sorry no imagery here" written on them, and the map zooms back out. This is in Hybrid and Satellite mode, the road map mode works properly.
You're right, different zoom levels show different missing tiles. Some levels are more complete than others. I just thought it was odd that this seemed to come with the release of 2015.12, for me anyway.
Perhaps a related issue. The offline problem has gone for me, though now I'm getting quite a few "Sorry, we have no imagery here" tiles. I have never seen these before. They are in locations that did have imagery in the past.