"Auto" video quality doesn't change to higher quality ever.

Hey,

So I have my player set to "Auto" and usually it's fine, it'll pop up to High or HD. But lately it's just stuck on the super pixelated low, even though the grey loading bar preloads heaps of the video. If the video is preloading up to 20 minutes ahead with no issue, shouldn't it shift to a higher quality stream?