FYI, ConBee USB adapters are kind of infamous in the community for having issues connecting over serial after reboot. Not quite sure that the root issue is for that (perhaps buggy serial drivers for the Serial-to-USB stack that ConBee USB adapters use or bug in pyserial), so if still have issues after the firmware upgrade then recommend that you consider opening a new issue with ZHA debug logs to the Home Assistant core repository → Issues · home-assistant/core · GitHub (also see https://www.home-assistant.io/integrations/zha#reporting-issues and https://www.home-assistant.io/integrations/zha#debug-logging)
Other general suggestions that you should really do regardless for improved setup and environment:
- Upgrade the firmware on the ConBee adapter.
- Connect your Zigbee Coordinator USB via a powered USB 2.0 hub, and use a very long USB extension cable. Note “powered” and “USB 2.0” as the USB-hub having its own seperate power-supply will secure its power source and connecting or even being close to USB 3.0 ports and other devices/cables are well known to cause serious interference to Zigbee.
- Add a few “known good” dedicated Zigbee Router devices (a.k.a. Zigbee Signal Repeater products).
- Follow additional advice in Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage (which include recommendations of “known good” dedicated Zigbee Router devices).