I have set up several encounters ahead of time, and whilst giving a friend a tour of one of my maps, with monsters hidden on the GM Layer. However, He was able to see the monsters despite this. I have checked several times that the monsters were correctly positioned, going so far as to switch them to the token layer, then back again.
Is this something that has to do with the Engine switching?
If this issue is through some oversight on my part, I am sorry.