After a period of not engaging with my four P110 plugs (during which time I installed the app on my new Android mobile), I noticed that the plugs were not 'live' in the app. After some time checking and re-checking everything I could think of, I decided to remove and re-install the one unit that was physically accessible and not in actual use. However, it refuses to pair.

Some observations:-
Eventually, the plugs became 'live' in the app. Sometimes not immediately, and sometimes not all of them, in a random manner, over a period of a few days. However, for a couple of days now, all three have been active in the app when I have opened it. They appear to be working as expected.
My many attempts to add the fourth unit have been characterised by the app not automatically connecting to the device and not having access to the internet when connected manually. I have no idea whether this is significant or not. The WiFi network is found and I am invited to supply the credentials to connect to the network, which goes through fine. The app finds and connects to the device but will not pair. All of this, btw, is within a metre of both the device and the router.
I have tried the Bluetooth on/off routine suggested many times. I also found a switch on the phone settings to allow Tapo to access 'nearby devices' but that has not solved the problem either.
After 'thousands' of failed attempts, I am at a loss as to how to install the P110. I bet the solution is simple. Alas, I have not yet found it. I need to crack it soon because at 85 I may not have much longer and in any case, this is not how I want to spend my dotage!

Best regards,

Limeyard