Why does AdBlock suddenly not work anymore?

Today from one moment to the next AdBlock suddenly stopped working. I have the latest versions of both AdBlock and AdBlock Plus. I've tried turning the extentions on and off, restarted the Chrome browser multiple times and even reinstalled it, as well as restarted my PC, but to no avail. Now every single YouTube video starts with not just one ad, but two, and often not even skippable, so the site has become practically impossible to use. Has anyone else been having this issue? Any idea what's going on? Is this just a temporary bug?