@D.D. 

This could be related to a setting called 'Fade Off' you could check if you have set up Fade off in Schedule settings and set is on Instant ON/OFF.

How to use offset and fade rate feature when schedule sunrise and sunset in Kasa app

In color Preset, if you set  Auto-White, the bulb will adjust to appropriate brightness based on the time of day. For a test, you could set a preset of your preferred color and brightness and see if this stops the behavior Changing Presets and Default State for your TP-Link Smart Bulb

 Hello  @D.D. 

Auto White/ Circadian mode follows your body’s circadian rhythm, as my understanding, the bulb adjusts brightness and color temperature to help you be ready for a sleep in the night. While you wish the light become brighter as the times goes by, which is a different feature, you could try to set a Schedule and set Fade On for the bulb as the workaround. 

  Hello @D.D. 

This would be a useful feature and i'd recommend start a thread in our Kasa Feature Request Board, there you could make a new feature request and users who like this idea could vote and comment for it. This helps us organize your feedback and share with our team for evaluation. 

Here is a Summary of most Popular Feature Requests for Kasa that you might be interested. Thank you for your time with the improvement suggestion~