Hello  @gunterzielke 

thank you for reaching out to the community and letting us know about the issue. 

It's a good step to factory reset the bulb to ensure that the problem is caused by Schedule/Away mode/Smart action settings in the kasa APP. 

If you use any third party apps like Google/ Alexa or other smart apps, please remove the device from the app temporarily to help isolate the issue. 

If the same issue occurs, can you share the MAC address of the device with us via PM. To look into this, please help provide the exact time when problem occurs eg, Jan 23th, UTC+1 ， bedroom lamp turn on itself, thank you. 

If the device is under warranty and diagnosed to be faulty, after troubleshooting, you can get a replacement under warranty period/

  @gunterzielke Thank you for letting us know the device is inRMA process, hope the replacement unit works fine, Feel free to let us know if you need any help~

  @mrkmax 

Hi, it's required to do some troubleshooting before RMA to confirm the bulb is faulty, and if the device is under warranty and confirmed is faulty after troubleshooting, you can get a replacement.

In this case, have you tried to factory reset the bulb and then reconfigure it? If not, please have a try.
How to reset TP-Link Kasa smart bulb?
How to connect TP-Link Smart Bulb to my home network via Kasa?

The above step is to ensure the problem is not caused by Schedule/Away mode/Smart action settings in the Kasa APP. If you use any third-party apps like Google/ Alexa or other smart apps, please remove the device from the app temporarily to help narrow the issue. 

If the same issue occurs, can you share the MAC address of the device with us via PM? To look into this, please help provide the exact time when the problem occurs, eg, March 29th, UTC+1, bedroom lamp turns on itself. 

Best Regards