Fab,
You are welcome. Thank you for providing more info. I know nothing of the Harmony Hub. If it works for you, then good. I might remind you that ALL these devices are now computers. It is kind of amazing that they "play nice" with each other as it is. And, firmware seems to "upgrade" without warning. Interfaces can change over night.
Regarding the Onkyo - refer to page 115 of your owner's manual at the upper left: 5. Hardware 1. HDMI Change the settings of the HDMI function. HDMI CEC (Default Value: On) Setting this to "On" enables the input selection link and other link functions with HDMI-connected CEC-compatible device. When this setting is changed, turn off and then on again the power of all connected devices. • Depending on the TV to use, a link setting may be required on the TV. • This function is effective only when the device is connected to the HDMI OUT MAIN jack. • Setting this to "On" and closing the operation screen will display the name of the connected CEC-compatible device and "CEC On" on the main unit’s display. • When this function is set to "On", the power consumption in standby state increases, however, the increase in power consumption is minimized by automatically entering the HYBRID STANDBY mode where only the essential circuits operate. • If you operate the MASTER VOLUME dial on the main unit when this setting is "On" and audio is output from the TV speakers, audio will be output also from the speakers connected to this unit. To output audio from only either of them, change the setting of this unit or TV, or reduce the volume of this unit. • If abnormal behavior is observed when this is set to "On", set it to "Off". • If a connected device is not CEC-compatible, or if you are not sure whether it is compatible, set it to "Off". On When this function is used Off When this function is not used.
Check to see if your setting is in default/ON. If it is, turn it off and see if that helps.
Regarding the LG C2, I noticed the same issue, having set-up all the apps on the LG without need of AppleTV, a Firestick, etc. The default seemed to go to the screen you describe "home dashboard". However, since my client had a couple of devices she used from time to time, she doesn't mind hitting the "home" button of the LG Magic Remote to see her apps at the bottom. It is slightly disorienting at first, but I think your wife can adjust pretty readily. On my system, with a C1, like I said, I run all devices through the Denon receiver. Thus, when I turn on the LG, it immediately shows whatever device that is selected on my Denon, which is usually AppleTV. So, I see the beautiful Apple 4K scenic screen savors for my opening screen.
The bottom line is: do not expect perfection from any device. Design your system (with all app preferences and hardware) set to your utmost liking as possible. Then, orient yourself (and your wife) to that paradigm and be happy with what an awesome AV system you own. Enjoy the heck out of it. And, be prepared for changes and shifts within the firmware and app updates. Some may be great, some, not so great. Life is complicated and so are AV systems. The better the system, the more complex, the more attention is needed by the consumer. Expecting to set it up and forget it won't cut it anymore. I doubt you want to go back to the era in which I grew-up: a TV with an on-off button, a dial that found 3 channels, if the antenna on the roof was positioned correctly. It was simple and required no further action once the antenna was set. But, I don't want to return to that era. Do you?
I hope you truly take the time to really enjoy your "fabulous" home entertainment system You did good!
Mr. Black
p.s. both of my subwoofers have been on for over 3-and-a-half years without interruption.