So, I've had the same problem as everyone here for a few months now.
While I can't be certain that it wasn't a software update that caused the connection between the televisions Smart Hub and my router to start going haywire, I am pretty convinced for me it was because I had an upgrade of my router just before problems started.
My old hub was years old, and so I assume only worked on 2.4ghz. My new one has the capability for both 2.4 and 5ghz frequencies. From looking at previous posts, it seems the tv has problems with newer dual band routers, and 2.4ghz is best for stability.
After going into my own router settings and switching 5ghz capability off, then going through the setup on the tv again, everything works perfectly and as fast as it ever has, with YouTube videos booting into life near instantaneously. I'm averaging 40 to 60ish Mbps in a small house, router about 20 meters away but through 2 walls. No problems.
Fingers crossed this is now fixed, and I'll update of anything arises.
Of course, of you have other devices on 5ghz, you can create a separate guest wifi just for the tv to enjoy the benefits of whatever you prefer (see above), but I have to say my creaky old Macbook is much faster at loading webpages since the changes also.
Seems the upgrade in stability doesn't affect speed for me much at all.
Worth a try. I had got so frustrated that I was looking at buying a wifi repeater with Ethernet, a Cromecast for smart functions or even getting my IP provider to move the internet connection to behind the tv and connecting directly to Ethernet to sort it. Glad to have seemingly saved the time and money.
