Flickering UI (Buttons) only while using the HMD, not in the game view at my screen

So, I wanted to improve the graphics of my project, because while using the Htv Vive, my game looks significantly worse. I don't know if it is normal. My Game view looks really good and I already checked some Optimisation from this page https://unity3d.com/de/learn/tutorials/topics/virtual-reality/optimisation-vr-unity (like MSAA or eyetextureresolutionscale).
Nothing worked so I've read something about "The Lab Renderer". I imported this Asset, but I noticed it is kinda obsolete and I wasn't able to do anything in my project anymore, so I deleted it immediatly (was hard because it reimported itself over and over again).
Now it is even worse since my buttons flicker now very hard when I move over them with my Raycast Pointer.
I feel like something from The Lab Renderer is causing this issue, but I think i deleted everything of it from my pc.
So, I am okay with having worse graphics than in the actual game viel while using the HMD, but the flickering (which also only happens while wearing the HMD) has to stop. Can someone help me?