Dynamic Lighting not Working for Player

So, last night I was running session using dynamic lighting on my maps to hide away areas outside of a player's line of sight, and it came to my attention that one of my players was able to see the entire map, totally illuminated. Dynamic Lighting was enabled, as was "Restrict Movement" and "Enforce Line of Sight." Even stranger, the system was working totally fine for my other players--they could not see anything walled off or unlit. Any ideas as to what could have caused this?

There have been issues where players with slow internet connections or limited bandwidth fail to load the dynamic lighting properly. A simple refresh of the page at their end usually solves it but that does rely on the players honesty. If you are aware of a player having these issues i would highly recommend having fog of war on with only a small section revealed for the first instance of a map, once you are sure it has loaded correct for everyone you can then switch it off... it also makes sense to have all of your monsters on the GM layer to begin with as well just to avoid that awkward 'don't go in there, there is a dragon waiting' moment ;) Not ideal i know but there isn't a lot that can be done when players have slow internet... if it isn't as a result of the known issue and it persists even after refreshing please post back and we'll look at the more technical reasons.