So we encountered a curious situation... because I like to play I let one of my friends GM a game using my account, and in his game, out of "nowhere" all of a sudden one of our newer players could no longer see the map - it went full black. He had just installed VTT, so we had him remove that, and reinstall it - nada. We had him try different browsers, nada. Fiddled with every possible setting on his token affecting sight, nada. Tried playing from a different machine.... still nada. So, because I diagnose things for a living, I logged back in as GM myself, and took a look. Turns out my friend GMing had inadvertently split the party by dragging this players token to a different map - one which we had not been to yet (so it was still all fog of war covered). Once I moved him back to the map with the party, all was well. Figured I'd share this for future generations, as when the group was googling we found plenty regarding all players not seeing the map, but nothing on just one.