SK6812 RGBW + Wemos D1 suddenly cycling colours

Hi there! I have a strange problem: SK6812 RGBW-Strip as Ambilight was working fine for more than 1 year with WLED on a Wemos D1. Suddenly, when it is switched on, the whole strip is flashing in cycling colors: The whole strip switches from red to green to blue and it looks like some kind of wanted effekt. When I send I WLED-command, the stripe obviously starts flickering. When I set it to black, the whole stripe turns black w/o flickering. Then, sometimes and without changing anything it works for some time and the problems start again.

My inital thought was, that some other app/ program suddenly interferes with the strip, but I could not identify any. I assume, the hareware-setup is just fine, because it worked flawlessly for a long time.

I exchanged the Wemos D1 with another one, but problem still persists. Has the strip gone bad? Could this be a possilble effect? Is something sending data to my strip?

Any idea what to do?