By the way, have you tried just reinstalling YouTube? I have an iPad 4 still on iOS 6 and both YouTube and Netflix apps still work (albeit, the apps haven't been updated in forever). The Netflix is good to have since Netflix on iOS 10 doesn't allow screenshots anymore.![]()
Netflix still working on 1st-gen iPad on iOS 5 even.
I bet your iPad 4 on iOS 6 is faster in many ways than an iPad Pro on iOS 10.