My Roku Streaming Stick+ appears to have a flickering problem.
I have a Toshiba 49U6763DB with Roku, Switch and Virgin Tevo box connected on HDMI.
Regardless of which port the Roku is plugged into, I see occasional flickering. It's hard to describe beyond "flickering", literally just a flash off and on.
It's particularly bad on Amazon Prime, but happens on all Roku channels.
Neither of my other HDMI-connected devices flicker in this way (ever).
Before moving house, I had the Roku plugged into a Denon AV receiver - and it had the same problem. I'm not sure when this started, it's possible that the device has always had such an issue, but we never used to watch Amazon Prime much until my son got into Thunderbirds, so that's when we noticed.