I had the same problems especially with Apple TV.
A CEC blocker solved the problem.

I have a problem with the Harmony powering on again after I have turned it off. The problems started after the latest software update of Harmony.

I have not completely pinpointed the issue and have send multiple scenario’s in which the problem occurred reported to B&O.

When I watch through the ATV and switch the Harmony off, it turns down and directly after switches on again. Sometimes it turns off and after a minute or so it starts up again. I found out that when I switch the ATV off in the apple menu, the Harmony switches off and stays off. But in this procedure the LG logo pops on the screen.

I think there is an software issue with the Harmony, it somehow sees active sources (apple tv switches off automatically after x hours) and starts itself again. This glitch occurred also when listening to myMoment through multiroom, the Harmony restarted somehow itself.

All in all the Harmony has made itself unstable and my guess it is related to latest software update and mismatch between sources it ‘sees’ when / while turned off.

Maybe anyone else is encountering strange behavior on the Harmony lately.

Hope this helps.

Serge