Which exact Zigbee Coordinator model? The Sonoff "ZBDongle-E" or the Sonoff “ZBDongle-P” model?
Regardless suggest test upgrade Zigbee Coordinator firmware (but perform a backup first so can revert back if get worse result).
Also recommend read and follow → https://community.home-assistant.io/t/guide-for-zigbee-interference-avoidance-and-network-range-coverage-optimization/515752
You should take note there that Zigbee can be extremly sensitive to EMF/EMI/RMI interference and you should follow the recommendations about taking actions to avoid it.