Okay. So here’s what you need to do!
It turns out we were barking up the wrong tree, the problem lays in your line trace, not in your network programming! You’re trying to set visibility to false when there is no stored variable for the previously line-traced player!
So what you need to do is when you hit the other player with the line trace, store them as a variable. Maybe “Last Player Seen”. Then when you go to disable the visibility, you use “Last Player Seen” as your target of Player, grab that health bar widget from them, then set visibility to false 
If that isn’t it or you need more help, please provide code for your line trace so we can straighten that out! 