Just some advice, I think that issue is cause the unity internal resolution for WebGL Exports is 960x600. I'd advice changing the Unity Canvas setting UI scale mode from "Constant pixel size" to "Scale with screen size" so it's the same regardless of resolution an aspect ratio. It's basically magic and I don't know why It's not default. Also, run your game in whacky resolutions and aspect ratios to look for misbehaving HUD elements. It really fixes a lot of your players HUD issues regardless of what monitor setup they have