Yeelight Serene Pro WLAN does not appear after reset


I tried do connect the Yeelight Serene Pro wit the Yeelight App and also with the Mi App. But it seems something goes wrong.
After Pressing the Reset Button for 5sec:

  • Light starts to flash
  • Light turns off and directly on

The settings seems to be be reseted, but it doesn’t gernerate a WLAN (yeelink-light_xxx) therefore I#m not able to connect with the light. I have the feeling something is wrong with the Lamp, becaus it turns on automatic after reset and also when I unplug an plug-in again. According to the manual it should be turned off in those situations. But I have no idea haow to solve the problem, or is it a defect?