Jonas Gessner, developer of ProTube:
I am very sad to announce that ProTube was removed from the App Store by Apple on September 1, 2017. This comes after multiple requests and threats by YouTube which ultimately led Apple to suddenly pulling the app from the App Store. ProTube and many other 3rd party YouTube apps on the App Store have been targeted by YouTube with takedown requests.
YouTube first requested Apple to remove my app well over a year ago, initially just stating that my app violates their Terms of Service. This was a generic takedown request they sent to many YouTube apps at once. They later started going into more detail, even stating that I could not sell the app as that alone violates their ToS. They basically wanted me to remove every feature that made ProTube what it is – that includes the player itself that allows you to play 60fps videos, background playback, audio only mode and more. Without those features ProTube would not be any better than YouTube's own app, and that is exactly what they want to achieve. YouTube wants to sell its $10/month subscription service which offers many features that ProTube also offered for a lower one time price, so they started hunting down 3rd party YouTube apps on the App Store.
This is very sad news. ProTube is far better than the official YouTube app in nearly everyway, and now YouTube have finally got their way and forced it from the App Store.
My favourite parts of ProTube was the option to get an audio only version of a video, support for iOS Picture-in-Picture, and background playback, just to name a few.
I'm going to keep the app installed on my iPhone and iPad, but I'm not sure what (if anything) will happen to them because of the removal. Whatever happens to them though, there won't be anymore updates, and when YouTube make changes to the API, the app will sadly stop working.
I doubt there's any point in finding an alternative, as no doubt if anything is as close to the quality of ProTube, it will be shut down in the same manner.