Interference or rouge device(s) are normally to blame so start by following https://community.home-assistant.io/t/guide-for-zigbee-interference-avoidance-and-network-range-coverage-optimization/515752
And https://www.home-assistant.io/integrations/zha#defining-zigbee-channel-to-use
As well as → https://www.home-assistant.io/integrations/zha#best-practices-to-avoid-pairingconnection-difficulties