What effect exactly? Do you want to disable selecting backfaces with alt or just the visual part, semi-transparent faces?
I was able to reproduce it. It happens when you zoom to a face very close so it starts to get clipped and all vertices are behind the view. I’ll skip those faces during selection for now. Let me know if you find any other issue
Select Box X-Ray 2.0.8 beta.zip (109.1 KB)