FYI, It is also known that the antenna design used on the “SM-011 V1.0” Zigbee module by CoolKit is not properly designed and tuned causing poor Zigbee signal reception, and assume that the onboard Wi-Fi mounted close on the board without separation or shielding will also add further electromagnetic interference to the Zigbee radio.
It could have been a great hardware implementation of a Zigbee bridge/gateway if they had a better designed Zigbee module with a properly tuned antenna and only used wired Ethernet instead of WiFi.
ZB-GW03 uses same “SM-011 V1.0” Zigbee module by CoolKit but at least it also has wired Ethernet:
More expensive but better-designed alternatives are the Zigbee LAN coordinators by ZigStar and Tube
https://community.home-assistant.io/t/zigstar-zigbee-coordinators-and-routers/338586