Hello @Neil_Brownlee and @Eddie
I could solve my issue eventually. So here is what I did:
- Buy shielded extension cable
- Delete Deconz and ZHA from HA by hand, including all Databases and files that will be kept even after deleting
- Update my Deconz Conbee III Stick
- Setup a new Deconz Zigbee Network. ZHA still won’t work for some reason.
Again, thanks to you all for helping me solve the issue!