KNX Dimmer stopped working after migration from 3.4 to 4.1

So I enabled Web Developer tools on Firefox and can see, that when I move the slider, it sends one request to Openhab with 200 ok for the Dimmer with a payload of “0”.

After that any movement I do with the slider does not trigger any further request to Openhab. That can’t be right. I tried the same with Chrome. I also did the usual SHIFT-RELOAD in FF.
I would say it looks like a UI issue then?

This looks like the same issue: Not able to use OH-Slider anymore after upgrade to OH4 - #6 by JustinG
Same upgrade path I took.

He talked about hue emulation and this is what I can also see here on my dimmer (I already wondered what this is):

How can I delete this metadata? For the others there is “Remove metadata” but for this not.