Zigbee network failure

This trick solved the problem for me and other people:

Hold your Homey upside down for 1 minute to enter recovery mode.
When Homey enters the recovery, please go to setup.athom.com with a laptop or desktop.
Select your preferred language, Press the ALT (Option on Mac) button to make continue in browser visible and click “continue in browser”, shown in grey.
While entering your WiFi information hold your ALT/Option button and keep holding it until you get the “Download full update” option.
When this process is done, please press the button “keep your data”, and let Homey finish the setup process.

Hope this solves it for you too