Lightroom :: Map Never Comes Online And Usable

I can be online with a browser (Lenovo Thinkpad, lots of RAM, HD space) and have quick online response browsing to any Inet site. My six students with PCs and Macs using LR 5.3 in the Map module all get online by WiFi (Guest in the school building) in the same room. We're all on that same Guest network. At my home office with that computer, the Map module works perfectly on my WiFi LAN.
 
But in class, my laptop won't show the map that they are seeing. My map screen in the Map module is just black, and LR reports that the Map module is offline. The rest of the screen in that module looks normal. I test for computer being online at the moment = yes, and with wideband response. The connection is very good and responsive. The screen used to show the gray world map when it was offline, and recently the screen map area is just black. I disconnected the projector VGA cable, no change. 
 
This happens consistently, every week - in the Map module they see the map, I have a black screen. Hard to teach when you can't illustrate.
 
What is going on in just that computer with identical software to students' and just when on that network when everything else works fine on my computer and theirs on that network.
 
It doesn't look like a hardware failure. There has to be a setting --- ? --- but there's nothing in the Prefs or Cat settings.