People, the instructions on the link posted above are the exact steps I posted earlier in the link that gets to the same topic over the Galaxy Tab S forum. The only difference is that this new link takes you to download another apk (already outdated) instead of the one on the Play Store.
I don't have a Note 4 so I'm just entering here once a day, so I didn't see until now that some have tried what I suggested and didn't work. Let me tell you, the first couple of times I tried this with the Galaxy Tab S (same resolution options as the Note 4, up to 1440p) it worked like a charm, last time I tried, last month after an update it didn't work at first. I just kept trying and it finally work and it's still working as up today.
I remember that what I did was that after Clearing Cache and data and disable the App I force Stopped it and be sured that it wasn't on the running apps list, I didn't re-enabled again from the App itself and just went directly to Play Store and looked for Youtube, in there you will see the Update and Enable I think I just hit update and it updated and re-enabled it, if is not like that, just enable it there and hit update.
After that I had my 1440p option again, only annoying thing is that everytime you start Youtube, the first video you must go and select the 1440p option and in order to apply it you must restart the video from the same screen,
I must tell you that my brand new Xperia Z3 also had the issue when I got it last week, highest resolution available was 720p, I followed this steps on it, and it also fixed it, only difference is that just after I fixed it there was a new update last week, and for my surprise even after the update it was still showing the 1080p, where my Galaxy Tab S, every time there is an update I need to do this steps again.