Frient - humidity sensor - no humidity value


I am running Webthings on RPI4+Conbee2 with software/firmware up to date. All my things do work. But I got a new humidity sensor Frient HMSZB 110 ( If I pair it in Webthings, I can only read the voltage of the batteries and the temperature but not the humidity. If I use some Conbee/Phoscon app instead of Webthings, I can read also the humidity. If I breath on the sensor, the value keeps on changing, so I guess the connection between the sensor (Frient) and Zigbee stick (Conbee2) works and the problem is somewhere else. Perhaps a missing add-on? I have tried some but so far no luck.

I would be grateful for any ideas. Thank you very much.

phoscon app webthings