Hey there, since the last 4 hours I'm having problems with SmartTubeNext, the YouTube "start screen" loads normally and shows videos etc,but when I click on the video it just doesn't load or it loads few seconds and then the app is buffering to infinity. I noticed when I log out (out of YouTube on SmartTubeNext) it doesn't lag anymore and all videos play normally. The stock YouTube app works fine. I deleted cache, I deleted the app data, logged back in, still the same problem. Then I deleted the app fully, reinsalled, logged back in and boom still the same problem, log out and everything works fine. Is YouTube working on something to block third party YouTube apps?
Update to 15.78 and it should fix your problem.