There appears to be an issue with Lightroom Develop module rendering of Alpha Channel transparency areas in PNG files when 'Use Graphics Processor.' It's most apparent in PNG files with transparent areas of 50% to 75% opacity. The transparent areas appear lighter and the screen flickers when moving the mouse pointer from the side panel area and back over the image area. The same flickering is observed when adjusting any of the Develop module control sliders. The PNG file transparency appears normal in the Library module because the GPU is only used in the Develop module. TIF files with the same transparency settings do NOT exhibit this issue. More information at this post: https://forums.adobe.com/message/9389286#9389286
I see the flickering but only when passing the boundary of the RH Panel set and the cursor changes to a resize arrow for the panel. Is that what you are seeing?
I see flickering when the mouse pointer is moved anywhere off of the Develop module Loupe Window area and then back onto it. The flickering also occurs when adjusting any of the Develop module controls.