On starting/ joining server the video quality / resolution is very low or just a blank screen, however if you go into settings then select video you can see the image in the background change to good quality then all you have to do is close all the screens to get back to the game, no setting are changed. This happens about 60% of the time on joining and it also happens when you get hit by a AI zombie every time the resolution drops so all is pretty blurred, the fix is the same just click settings / video then close back to game screen and all is ok again. My video settings are Very High and res is 200%.