FYI, while many people reported that ITead’s TI CC2652P based “Sonoff Zigbee 3.0 USB Dongle Plus” (model “ZBDongle-P)” can be a better Zigbee Coordinator and is recommended for Zigbee2MQTT, quite a few people have reported that ITead’s “Sonoff Zigbee 3.0 USB Dongle Plus V2” (model “ZBDongle-E”) works better as a dedicated Zigbee signal repeater / Zigbee range extender if you flash it with Zigbee Router firmware and then power it with a simple USB-changer before you pair/join it to your Zigbee network → Sonoff_Zigbee_Dongle_Firmware/Dongle-E/Router at master · itead/Sonoff_Zigbee_Dongle_Firmware · GitHub
I highly recommend buying three (3) ZBDongle-E to re-flash and repurpose as Zigbee Router devices.
There is more related discussion about that here → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage
FYI, it is recommended to update to later firmware → https://github.com/Koenkk/Z-Stack-firmware