tier linking? you mean first tier or second tier? no need to complicate things if you mean basic linking.
I am also curious. Sounds to me like the CTR would lower.
Do not expect that seo's who pay premium will share with you for free.
Perhaps youtube penalty of some sort? For whatever happened on that channel. Doesn't look fit.
Is this some kind of a Google tradition now? Same thing last year https://seoforum.com/thread/possible-algorithm-update-january-2019