Hey all so I have had this same exact problem over the last week or so. Started one morning after I left Gentle Alarm on in night mode (usually don't do that) all night. Finally found this thread (thank you btw) and worked with LG Live Chat to process a RMA to get this fixed.
Got around to backing everything up, saving my pictures and my Nova Launcher settings, unmounted my SD card and was just about to perform a factory reset. I decided to uninstall Nova (Prime version) and now what would take at most a min; the screen flicker, freeze, and fade to black is not happening. I've only been testing this for the last 30 min, but this is the longest I have gone with out the topic issue.
I only saw Nova mentioned in one post, but seeing how laggy the LG launcher is, are most people here using Nova? I am holding off sending this in until after the weekend if necessary for more testing, but this seems really strange, especially since it looks (and acts?) like a hardware malfunction.
The only other thing that has changed between the last glitch fade besides uninstalling the launcher is that I don't currently have my SD card in.