The Roku Streambar I have in my bedroom started buffering in the evenings when I wanted to just chill and watch some TV. The obvious checks came up clean. Roku's own network test, found under Settings > Network > Check connection, kept reporting “Connection check was successful” with a simple OK button. My other devices streamed fine on the same network.
So the Roku insisted it was healthy while buffering two or three times an episode. The tool that I finally found is a diagnostic screen Roku ships on every device but never mentions anywhere, reachable only by a button sequence on the remote, like a cheat code for your own hardware.
Roku hides a full Wi-Fi diagnostic behind a remote code
Press Home five times, then Up, Down, Up, Down, Up
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