@RSEQ,

Can you double-check your available updates for the Kasa App? The team has been constantly releasing updates to fix bugs such as this. There are a few solutions that the community has found to solve some of the issues for now.

1 - Just Reinstall the app - Sometimes if devices register as offline, or not on the account, the fix is to just uninstall and reinstall the Kasa Application 

2 - Try deleting the documents and data associated with the Kasa app on your phone, this will clear your phone of any settings or data from the previous version that may have been causing the incompatibility.

3 - On the homepage for the Iphones Settings, you should find the Kasa application near the bottom, try removing the local permission and relaunching the app. This seems to be the fix that helps the most people, however, this will prevent you from connecting new devices to your account, the setting must be enabled for any new devices to be added.