Scenes can be added but are not working

I am using a Conbee II on a Raspberry 4 with Phoscon app (and Deconz in ioBroker).

I have two Tint-lights that I have included in one light group. I have set up scenes and everything has been working fine. Now, when I wanted to add additional scenes, I observed that new scenes can be added, but won’t work.
When I recall the scenes in Phoscon the sliders of colour/saturation/brightness show some random wrong state. The scene will not be started - no changes at the lights.

I have deleted the light group and added the lights to a new group. Here I observe the same behaviour. The first seven scenes are working. Bginning from scene #8 the scenes are not working.