The R7800 is capable of streaming 4k. With that being said, 4k requires consistent higher thoroughput than 1080p. That usually means if there's wireless interference, distance issues, multiple devices streaming at once, you'll probably have issues. I've made sure all my 4k devices are hardwired to prevent the buffering that would happen at my place. I have great signal but so much wireless interference that consistent high thoroughput was a struggle. I could pull 400 mbps on wireless but it wasn't consistent enough.
A couple things you can try.
1. Make sure its on the 5ghz band. It has higher thoroughput than 2.4ghz
2. Do a wireless scan to see if there's unusaged channels you can make sure your 5ghz is on.
3. HVAC, concrete, bricks, and some foil insulation can cause significant signal blockage. Sometimes moving a router a little bit can free up a path to devices and make signals better.
4. high thoroughput devices should be on the 5ghz band and lower thoroughput devices keep on the 2.4ghz.
5. Distance is an issue with any device. 5ghz doesn't reach as far as 2.4ghz. Optimally placing your router in the center of the house can make a big improvement.
What firmware is on your router? How big is your house?
Is it only one of the services that has issues or all services?
I'd try the channel change as well.
That model roku has a built in speedtest under your network settings. I'd run that and see what results you get. That'll help with placing and figuring out problems.
