This is just an FYI in case it helps someone:
I have a main P9 and a remote P9 (and a 3rd unused unit).
I followed the app suggestion to update this morning, everything was functioning before.
Afterwards my main unit functioned correctly (with presumably the new firmware 1.1.0) but the remote unit had a solid yellow led.
I tried resetting but still solid yellow led. (I also tried various pointless things suggested by support such as different outlets and changing power cords.)
I have an RMA so will hopefully be able to get a replacement before I return the unit (I still need to work!).
Not that it is relevant, but I configured the 3rd previously unused unit and it works fine. I will not be upgrading the firmware before the RMA.
I should know better than to upgrade.
Stay connected :-).