Make sure that not getting EMF/EMI/RMI interference from any other sources (as Zigbee radios are extremely sensitive to EMF/EMI/RMI interference from all different types of sources, not just WiFi), and also be sure to first add few good mains-power Zigbee products that act as Zigbee Router devices (also known as Zigbee signal repeaters and Zigbee range extenders) before you pair any battery-powered Zigbee devices, read → https://www.home-assistant.io/integrations/zha#best-practices-to-avoid-pairingconnection-difficulties and I also highly recommend try to follow all the tips here before troubleshooting any further → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage
If willing to live on the cutting-edge then could also try upgrading to a newer BETA-version of EmberZNet NCP firmware of the Zigbee Coordinator, but I would advise reporting the issue to get your debug logs analysed before doing so, see → https://www.home-assistant.io/integrations/zha#reporting-issues