We upgraded our router and hate to say it, our fix was to replace our Roku Streaming Stick+ with a Chromecast with Google TV - performance in apps like YouTube were fixed immediately (and, yes, we factory reset our Roku and it didn’t help)
To be fair, we made an attempt to ask Google and Roku to work together to fix their Roku YouTube app and both companies honestly have horrible tech support when it comes to issues like this. It’s very clear when you go to the Google YouTube support forums - it’s like they don’t acknowledge the Roku app exists.
I tested a new ROKU Ultra (model 4800) today over Ethernet that comes from the POE power adapter to the router… I was getting 20 to 30 mbps from the Ethernet when tested on my Mac…. Hooked it up to the Ultra and hit the SAME “<1mbps” from the network test !!! 😵💫😵💫😵💫… got a couple more attempts to try but it seems like a ROKU OS issue….. an hour ago I went down to the clubhouse and hooked up an Apple TV… 2020 4K model over Ethernet:.. ran the SpeedTest app… well over 20mb download… stay tuned 😎
My 4800 is one of the few Roku devices that actually report a reasonably accurate network speed. My Internet is 108 Mbps, so I can max out a Fast Ethernet connection. My 4800 will report 80-90 Mbps, which is right where it should be. But none of my other Roku devices, wired or wireless, come close to reporting them accurately.
The only Speed Test site you should trust is the site provided by your ISP.
Also, take into consideration that Roku puts the brakes on wireless AC. All 4 of my Roku wireless AC products have a line speed of 152mbps and not 866.6mbps with a strong wireless signal. 3 devices get 94mbps of download speed and one device a little further from my router gets 76mbps of download speed on the Roku download test. The only way you can find your line speed is in most cases is to logon to your router.
Even though Roku put a governor on wireless speed. I have not had any issues streaming anything across the internet. No issues with streaming UHD movies on Prime or Netflix. ESPN, Fox Sports, YouTube, NBC Sports, and CBS Sports all stream without buffering.