YouTube not working like before..

[AC Question]

YouTube help: Using a rooted htc m7, when was on android 4.4 YT was working flawlessly like it was buffering video in such a way that you can even quit YT and still it would not buffer again even if you watch a different video and come back it would still not buffer , this thing saved a lot of bites but now i upgraded to lollipop 5.1 and using the same version but this time it's not doing all that amazing stuff.. WHY