I'm also having this same issue on a Roku 4. Running the latest firmware. Would love to know if you or someone else has found a solution. I opened a support ticket with Roku a few days ago. If I hear back I'll update this post.
Same issue. It only occurs in 4K mode for me. If I switch to 1080p, it goes away. Amazon is the only app I've seen the issue with, so I contacted them to report it. They were less than helpful about it.
"Wynn" wrote: I get a flashing green line (sometimes white) at the bottom of my TV screen whenever I am streaming from Amazon or Google Play Movies. Flashes about every 20 seconds or so and is quite annoying.
Roku 4 (can't get the firmware version at the moment) Pioneer VSX-45 Av receiver Vizio m55-c2
I managed to get a little video clip of it if I can upload that somewhere. Anyone know a solution?
You can upload to Dropbox or similar website (or even YouTube). Just post or PM a link, and we'll take a look.
In addition to the above information requested, please also include any other peripheral devices that may be connected to your setup.
C. Shawn Smith
C. Shawn Smith Community Liaison
------------ The Cosmos is all that is, and all that was, and ever will be. -- Carl Sagan
Seems to be just a Roku 4 issue. I ended up upgrading to a Premier+ for HDR compatibility, and haven't seen the flashing line on any content. Unfortunately the Premier+ has it's own issues - purple HDMI Authentication error screen, audio glitches. Roku really needs to get this stuff straightened out.