A recent Youtube Web update has added a canvas whenever the seek bar is visible, an HTML5 canvas pops up. This was not asked for and not needed. If you disable canvases for privacy, this will cause a horrific red bad to cover half the screen until you hide the seekbar. Canvases can be used for fingerprinting, which I’m sure Google is doing here.
Sure sounds like it’s just an excuse, since it worked swimmingly before the canvas claim.