Players see black map - have to toggle fog of war on then off for them to see

Edit: Gauss gave me the answer - map pack add-on had dynamic lighting on by default, turned it off, issue resolved. Hi all, I'm very new, sorry if this has come up but had trouble finding my exact issue. Basically as the title states, when a player joins my game, they only see a black map (I confirmed the player flag is on the right map), however, if I turn fog of war ON, then back off, they can see the map just fine. Same result if I re-join as player. I also noticed if I preemptively turn fog of war ON, then back off before players get to the map, they can load in just fine, no black screen. I've had this problem on both games I created with my pro account. What am I missing? All players are on Firefox. Thanks

Is this in a purchased product such as a module or add-on? If so then it is probably Dynamic Lighting.  Turning Fog of War on turns Dynamic Lighting off. 

Thank you, Gauss. It was dynamic lighting, turned on by default on the map pack add-on I was using. Toggled it off, issue resolved.