I just experienced this with my last match where one of the enemy heroes ain't showing their HP bars. If the character just stands under something and stays in the shadow I won't be able to see where they are at all. I can't even produce a screenshot/video of the event because i turned off my game recording recently.
I've been getting the same issue. Though it's not constant, it's hard to determine exactly what causes it but occasionally enemy health bars disappear for a while. Allies too. The hp bars come back, they're not gone for the rest of the game when they go. Happened to Seven and Yamato last game. I think it has happened to me further towards the end of a game so might be an item or something that causes it.
