@SteRumbelow I'm having the same 'issue'. Everything appears to be working but the App suggests otherwise. 

@Bob12345 glad it isn't just me. It has happened again today and immediately shows a loads of devices as offline, yet they're all working perfectly fine with no interruption in performance. 

@TP-Link Thanks for this. I've upgraded the firmware this evening and it hasn't fixed the problem. Straight away, one of the Decos went offline (the unit never shows a light other than white, indicating there is no problem?). 
 

I've attached screenshots showing the problem and also showing the updated firmware (when the unit came back to life briefly). 
 

I chose to do the upgrade this evening because two units had gone offline and wouldn't reappear. The only thing that got them back online was taking the power cable out and replacing it. Neither of the two satellite units lost internet or changed to a different colour LED, but both showed offline in the all. Refreshing was unsuccessful and this was shown through the web interface too. 
 

I refuse to believe this is a proximity issue. The main Deco is down a set of stairs, the second is in the bedroom upstairs which is 12ft (4m) above the main unit and 4m to the right. Diagonally, it isn't more than 5 metres away. The final unit is in the living room, which is also upstairs but no more than 10 metres away. 
 

Please help! This is super frustrating. 
 

In this first picture, you can actually see two of the Decos! They're so close together, so as I said, it cannot be a signal issue. 

@SteRumbelow Having played around in the app this more since my last post, this issue definitely isn't fixed and it's incredibly annoying. 
 

Decos are still going offline completely at random and without reason. Devices show as offline when they are very much online, connected to the network and with good speed. 
 

The Deco units only show white lights, never red as the app would suggest. 
 

Also: why have you marked this as resolved/having a solution? It might be worth waiting to see if your fix actually resolves the issue - because it hasn't, in this case. 

I'm having the same issues, Decos P9 randomly disconnecting with the same error, nothing helps. How long til you guys release a firmware (officially) that fixes this problem?! I'm about to return for a refund if not soon.

Having had a few days keeping an eye on the app everything seemed to have resolved itself. Then, this evening, one of the satellites is offline again. 

But it's not. It's fine and working (white light). And I can tell because a. The laptop hard wired to it works fine and b. If it unplug it the signal drops in that room.

Why is the app misreporting the satellite performance?