In June 2024 I had to replace my receiver, so I bought a Marantz NR1510. I had no difficulty changing the Harmony app to accommodate. I set up 4 activities: Cable; Roku; Blu-ray; & FM Radio.

It worked fine for 3 months and then went haywire. If I launched the Cable activity, it looked normal. But when I hit a button (eg, Cable Guide), the Marantz would change input from Cable to Roku. Other buttons caused the same weirdness. I managed to factory reset the Harmony's remote & hub, but that would last a day or 2 and then revert to madness.

Convinced that either the remote or hub was toast, I found a guy on eBay selling new-in-box Harmony Elites. After paying way too much (don't ask) for the new one, I would up in the same boat: set-up goes fine, but after 2-3 days, remote chaos.

Since the Marantz receiver component change seems to have brought me to this insanity, I suspected that it might be the issue. But it and every other device works perfectly when I use the original individual remotes.

I'm stumped! Please help!!!

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.

​Mostly, the IR trash simply slowed response because the trash was interpreted as invalid commands by the devices, but occasionally there would be an incorrect response because the command was modified by the trash.

With respect to ROKU commands switching inputs on the receiver, this is probably caused by CEC and your old DENON probably did not support CEC. A CEC blocker inserted into the ROKU HDMI cable might resolve your issue.