I've had the black health bar issue for a while now, I know how to fix that. If you have your league on fullscreen I heard that you can just alt+tab out of league and it should work. (Didn't work for me)
If you're like me and have your league windowed or borderless, you have to go to your video settings in game and look at the "Windowed Modes" Options. Switch Between any of the 3 options and revert back to the way you had it to fix the health bars.
You have to do this EVERY Match also. It's tedious and annoying.
It also doesn't fix the loading screen because you can only change your video settings in game.
Riot hasn't had a fix for this yet. I also keep hearing only laptop players are effected by this (which shouldn't be an excuse for Riot, I've NEVER had this problem until the past month). I really hope Riot Fixes this though, this is a really annoying problem.
[zombie-nunu-tears]
PS: You're not the only one with this problem just to let you know. :)