I use Ublock on Safari as my only extension and it always worked great but, as of about a month ago, most of the time now I have to hit Disable Extensions, then reload the page, in order to watch a video. If I don't, I just get a black screen soon as the page loads (not the entire screen, just where the video should be). Every several videos, with Ublock enabled, it lets me watch it like normal while blocking ads.