IKEA TRÅDFRI wireless dimmer not changing lights

Hi
I recently migrated from Conbee 2 to Conbee 3 and used the backup function to migrate.
Most devices worked fine.
Including all my IKEA TRÅDFRI wireless dimmers, the very old(!) round ones.
Most of them still work.
But a couple of them I had to re-pair, and for these the lights do not react when I turn them. I can see that the switches blink in Phoscon so at least deCONZ can hear them.
I add the lights to the group in the old web app, then the dimmer shows up in Phoscon as a group.
But the lights in the switch group do not react. I tried both with IKEA and Hue bulbs.

I think it is an issue with the database or the device itself. At least I could re-add another dimmer and it works fine.