I've encountered some weird issue where from time to time a video in the YouTube app will say it can't play as the device doesn't support the file type. I'm guessing your phone is automatically filtering the results so that it shows only the videos that will be able to play on your phone.
This is strange and I don't understand it because the iPhone plays YouTube video. So I don't get why some play and other don't. I noticed this same issue when trying to watch YouTube videos on my Tivo. Some of them show up and some don't.
YouTube has had a long-standing issue with the subscription box on every level imaginable. Sometimes videos don't show up, sometimes they keep re-appearing, sometimes they won't go away period. It's just something they haven't yet perfected.