@Meshdave 

I have exactly the same in my M5

@mr.dos I've figured out it's any time any device connects to the main deco, it generates another new device notification. When they connect to the other two decos, it doesn't. 

@Kevin_Z Hi. It is any client - two different android phones, smart plugs, smart bulbs, our heating system, anything that connects to the main deco gets reported as a new device - but, as I said, with any customised name still in place.

I confirmed it is when they connect to the main deco only by looking at the reported devices in the app. Normally not much connects to the main one, but after the upgrade I had many notifications, I presume because the main one was the first to reboot after the upgrade. As I have not had the system long I just assumed this was a result of the upgrade. The next day I received 2 more for 2 of the same devices, and I then realised these were the only 2 that were connected to the main unit. So then I did some testing to confirm.

I can reproduce the problem any time by plugging something in, or turning wifi off and on again on my phone, when standing right next to the main deco, and confirming where the device has connected. If I move away to near other decos so that it connects to them and not the main unit, it does not happen. I have power cycled the system, made no difference.

My original router is a combined router/modem, so I cannot test connecting the deco directly to the modem as you ask, I don't have a separate modem. This is why I run in AP mode.

I only bought the M5 from Amazon just under 3 weeks ago. On the back of the unit it says the FCC ID is TE7M5V3, and it also says EU/3.0 after the serial number, does that mean V3 hardware?

I am lucky, this is the only problem I have and apart from this the system is still working well. But judging from some of the other problems being reported, others are having much more serious issues, it looks like the quality of coding and especially testing of this update is really very poor.

@Meshdave 

I have the same problem (and many other people as I noticed on the forum) after 1.4.0 and noted it in another thread as well.

It happens to me with devices that aren't even disconnected to the system too. Maybe it has to do something with the modem/router that renews the lease for a connected device and that the Ddco experiences it as an new device' (probably a bug). 
I run in AP mode as well. My modem renews leases every day.

Edit: Just now I got 2 messages of the same device on the same time stamp. This is getting odd. Luckily it doesn't send me push notifications;)