I ran into this problem as I noted in one of my other posts.
I chatted with a support person from TP-Link. My connections worked fine for years, then two days ago suddenly stopped getting a good Internet connection, even though the Roku device said there was an excellent connection to my WiFi router.
The TP-Link support person suggested changing the channel assignment in the router from "Auto" (where it was connecting to channel 6) to fixed channel 11: then reboot both the router and the Roku at the same time (I gather this is to get them both working on the new channel).
This solved the problem for a couple of hours, then the connection slowed. On my own, I went into the router again and changed it to channel 10, and I also changed the bandwidth setting from 20 MHz to 40 MHz. I then did the "test network connection" in my Roku and got the highest speed connection I've seen for this device. It has been working well for a day and a half, so for now I have a solution.
TP-Link didn't explain why the change, but it's possible that some source of interference popped up that was causing problems on channel 6. I ran a program called WiFiInfo on a Windows Laptop: it will tell you about all of the WiFi connections your computer can find (which can be very interesting in itself). It showed only me on channel 10, so that might be part of the solution. I did not do any tests to see if changing just the bandwidth makes a difference.
So if you're getting a good connection to your WiFi router but bad internet from there, but your PCs and other devices have a good connection to the internet, I suggest you try changing the WiFi channel on your router and see if that helps. If not, you can always change it back. You might also try one of the programs that tells you what's going on with all of the WiFi connections near you to see if lots of people are using one particular channel, and stop using that channel yourself if you can.
