Well guys, I have two samsungs, a "smart hub" and an "android tv", and I'm having the same youtube problems in both of them.
I had some issues with them so I talked to Samsung official Support for my country, I was so upset that I was going to legal plaint against them and the seller, so they sand a tech to my house, not an "subcontractor", a real samsung employee for my country.
Samsung guy was very kind and helpfull, and repair all hardware issues but he said:
"all samsung smart tvs have several issues whit apps, no matter if Android or Smart Hub, but smart hub is more unstable"
He recomended me to use cable connection (not wifi) because all samsung tvs NIC (network cards) are crap.
About youtube he just recomended to uninstall and reinstall the app from android TV, it works on them
But in some "Smart Hub" tvs (like mine, j5200 2017), you cannot uninstall Youtube because it is built-in, and if you reset all the tv, it will auto-update when you get it online: SO THERE IS NO SOLUTION FOR SMART HUB: Just await an update from samsung or youtube ...
The most awful thing that the Samsung Tech told me was that it is more likely to samsung or YouTube stop supporting "Smart Hub" app than give a final, and stable-full app. In fact several apps for "Smart Hub" no longer works by ending support from samsung or the developers.