When using a campaign on Dnd Beyon'ds MAPS for in person play, I have an HDMI out to a second screen which a digital table top we use for the minis. However the Maps tool will randomly just stop working, and I'll have to refresh it on the DM side, reload it, then stop the game, pull up the map then drag it back over to the digital table top again, which is pretty frustrating as it happens often. Has anyone else have this issue?

Everyone does because it's a deliberate in-built feature for resource management control. You're using the maps tool in a way it was not intended. You're meant to be using it frequently - as in players using the maps to move their tokens and you moving monster tokens and scenes and fog of war - so to save resources it will time out the session if nothing happens for an extended period of time. This is deliberate intended behaviour, not a bug. 

I'm looking into doing the same thing - casting player view to a projector for in-person play. Is this 'intended behaviour' still an issue? How long until it times-out? It would be nice to use the fog of war but this might be another reason why I can't use their maps. I can always use offline files and cover the fog of war up with pieces of paper but honestly I thought we would have a more sophisticated way of doing this by now...