My internet isn’t the fastest, but it’s not THAT slow. Every time I disable Avast shields, the videos load normally again. I’m not sure if running Avast Free and Malwarebytes Pro at the same time is causing the problem.
I’m also facing slowdowns at YouTube with version 8 beta. I don’t have MBAM.
Maybe the programmers could check from their side also.
No slowdowns noted here, and it would be very evident on classical music ;D
No slowdowns here at all , everything is perfect.
I had slowdowns with Bitdefender earlier , that’s why i switched and bought avast! 
I did not notice such a slowdown ATM.
I don’t watch a great deal of youtube videos, but those that I do don’t appear to be slow.