It is not a “repeater” (that is the wrong technical name), it is a Zigbee Router, and that is not what a Zigbee Router device does. Zigbee Router will consolidate messages from devices behind it and as such off load the Zigbee Coordinator and build out the Zigbee network mesh. Zigbee depends on “network mesh” technology to expand the network with more devices. Read → https://www.home-assistant.io/integrations/zha#using-router-devices-to-add-more-devices (and https://www.home-assistant.io/integrations/zha#introduction)
Follow tips here about avoiding interference and adding more “known good” Zigbee Router devices → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage