You lose vision if you die, you lose vision if you get revived. I don't know the trigger but there is one trigger to make them all work again. Can't remember what I did or if it even was me that caused this trigger. Red dots in minimap and fog-of-war next to you also disspear since "there is no drone anymore" so it's not just a visual bug.
I remember back in 2015 when the Agent was op... Rest in supplies, my friend.