Looking at the HTML generated, there’s a transparent
<div> right above the map iframe that is overlaid on top of the map:
Removing that div in the debugger makes the map work fine.
Confirmed broken in Firefox 52.0 and Chrome 56.0, with several different URLs.
Some more background: I cannot reproduce this on another category. The bug happens under Staff.
Nevermind… I don’t know why it worked once. It consistently doesn’t work now.