I have been using the individual remotes that came with each component since my problems with the Harmony 10 days ago (something I had never done until now). Twice during that time, hitting the Guide button on my Fios remote caused my system to jump to Roku! The Roku screen that comes up is an attempt to add the Discovery + service; this was also the case when the Harmony caused the error.

I don't know of a way for me to "see" what codes are being sent by any of my remotes. I suspect that the Fios command for "Guide" is the same as or is close to the Roku command for "Add Discovery +." This doesn't really make logical sense to me: if they were the same it should happen every time; if they're close, how exactly does the code get scrambled?

I did a test to see what happens when I am watching cable and then hit a button on my Roku remote. When the Roku receives the command, my Marantz receiver changes input from Cable to Media Player. I don't think my old Denon receiver did that. So I may have had this problem all along.

Yesterday I reprogrammed the Harmony, and I assigned "InputCbl/Sat" to an unused button. If/when the error occurs again, I can jump right back to cable. If this doesn't work, I'll be back.