I have a Philco 50" Roku TV and after almost a year and in the last few days I noticed some horrible thin horizontal black lines, like you can see in these pictures. I'm almost sure this happened after the last automatic software update. I noticed some stuff has been changed, like the interface typefont and I don't know that to do to fix these horrible lines. I tried the reset to factory settings already, but the problem is still there all the time, not only when streaming, but all the time. Searching about this I've found another person with this same problem:
It looks like this is a hardware issue. Have you tried contacting the TV manufacturer to inquire further? I'd suggest starting there to see what options or suggestions they can provide. Each Roku TV manufacturer provides direct support and warranty services for their products running the Roku OS.