What it means
Zigbee2MQTT could not talk to the coordinator stick and stopped.
Why it happens
- Wrong serial port, or the port path changed after a reboot (/dev/ttyUSB0 ↔ /dev/ttyUSB1).
- Wrong adapter type: zstack for TI CC2652 sticks, ember for Silicon Labs EFR32, deconz for ConBee.
- The stick is busy: ZHA or another add-on already uses it.
- Old or wrong firmware on the stick.
How to fix it
- Use the stable path: /dev/serial/by-id/usb-… (Settings → System → Hardware → All hardware).
- Set serial: adapter: to the type that matches the chip.
- Remove the stick from ZHA (or stop the other add-on) before starting Zigbee2MQTT.
- Update the coordinator firmware with the vendor’s flasher.