Just in case you were getting comfortable with the YouTube app's latest design, it looks like there may be more changes in store. It seems a number of users are encountering a new YouTube interface, apparently triggered server-side without an app update.
The change sees YouTube's hamburger menu flipping right out of the interface, going the way of Google+ in discarding the left-side navigation drawer. Instead, users are given four primary tabs - Home, Trending, Subscriptions, and your profile. Interestingly, a couple of these tabs seem to have bars underneath to switch from, say, all videos to music on the home tab, or from uploads to channels on the subscription tab. Besides these changes, things are ostensibly working just like before.
For now it's unclear whether this change is destined for a wide rollout or just an A/B test, but if the interface is as easy to use as it appears, it may be a welcomed change. After all, the nav drawer in YouTube's current iteration includes a considerable 17 items not counting playlists or subscriptions. Add those in and my personal nav drawer has 60 entries. Pulling all those apart into areas of the app where they contextually belong may just be a good thing, but we'll have to wait and see how easy it is to live with the new interface.