Lost devices after changing channel

Configuration Zigbee
1

Hello, is is nomal, that devices are no more connected after change of channel.

2

Yes , Channel change == frequency change, one could say it's similar as changing Channels on your TV ... CNN and BBC don't communicate on the same Channel

So try to reboot/restart your devices
If you'r lucky the devices find their Controller again, if not you have to reset the devices, and add it again

3

What he said ^^

It's not explicitly explained in the ZHA docs, but Zigbee2MQTT docs make it pretty clear FAQ | Zigbee2MQTT

4

Thank you very much.