@WeathermanTed 

Two potential issues for this if all devices are being affected.  Either the cloud access is interupted or there is a issue with in your network and the devices have lost access.  A few things to try. 

1.  Try to access the devices from the same local network.  This will let you know if its a remote/could issue.

2.  Try to access via LTE, this will rule out remote network issues.

3.  sign out and sign back into your Kasa account 

4.  Make sure the app is updated 

5.  Make sure all of the devices are updated 

@Carl Thanks. I think I resolved this infrequent but irritating issue.

This happens when my 2.5 gHz WiFi goes down.  It might be related to when we go over our allotted usage with our provider or it could be random or related to something else.

I'm not exactly sure how I brought it back this last time but when I did, all devices were responsive once again.

@WeathermanTed, how did you rediscover? I can't see how to do that on the app. 

@Sheflower 

In the Kasa App simple press and hold on the screen and pull down to "refresh" the devices this will put a query of your TP-Link Kasa devices and show which are available and which are not at that time. 

@Carl, thanks for the tip! Turns out in the end my router needed a reboot after the wifi went out for a bit. But the info is good to have for future reference. 🙂

@Carl   your instructions are not that helpful...when you say try this..maybe explain HOW...otherwise it is techno babble!

@Carl 

WEATHERMAN TED:  how do you do the things you listed?

@Bobger 

1.  You are trying to control your devices in the Kasa app while on the same wireless network (local network) as the devices.  

2   You are trying to control your devices in the Kasa app while on LTE (remote network) or in other words your phones wireless turned off.  

3.  To sign out you simply tap on your profile and click sign out. 

4.  This would be going to your phone's app store and checking for updates

5.  Tap on the 3-bars in the Kasa app's home page (upper left), tap on settings, tap of firmware update and check if all devices are up to date. 

Typically, especially in a forum environment functions considered to be basic or general functionality will just be described without further instructions as it is assumed by general consensus that the steps will be understood.