@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 

@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. 

@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.