Videos randomly turns completely gray
Solution 1:
Try playing with the file caching setting.
Tools > Preferences > Show Settings: All (bottom left) > Input/Codecs > Advanced section > File Caching
I changed it from 300ms to 1000ms and it fixed the problem. I suspect the grey screen issue happens whenever VLC fails to get the video data from the drive fast enough (slow drive/other programs accessing it).
Solution 2:
I had this problem. It seemed like VLC was using too much CPU. Solved it by installing the 64bit version of VLC. vlc-2.2.1-win64.exe
Solution 3:
I found out that playing a video in VLC that is being accessed by another program, uTorrent in my case, would cause multiple grey screens throughout the playback.
I either closed the program (uTorrent) that was accessing the video or stopped it from using it. I restarted the video and no more grey screens appeared.