Hello @troost, I have no time to investigate your case (and without code, it would anyway be impossible), but maybe you can try my (basic) library for PM sensors here: https://github.com/Nca78/NcaPMSensorLight to see if you have a similar result with it.
Nice graph. I will do something similar in Grafana. I think my MySensors device should also report every minute, perhaps using the highest sampled value. All values are sent to MQTT by my gateway and my Home Automation will store the time value pairs in influxdb. Right now I'm waiting for the hardware to arrive...
@bjacobse I was surprised too as like you I had seen that they would not work with mysensors and definitely not with debug output - with 2 switches I was able to use debug output, but not after adding the htu21d (which I expected to fail, but after a little code change worked well). We live, We learn!