Relative modern Zigbee Coordinator adapter like those based on Silicon Labs EFR32MG21 or Texas Instruments CC2652/CC2652P radio chips can handle around 200 Zigbee 3.0 devices if you have enough Zigbee 3.0 router devices, see:
https://www.home-assistant.io/integrations/zha#using-router-devices-to-add-more-devices
and
Try replacing the battery with a new one so not a batter issue (low-battery reporting from battery-operated devices are often wrong so should not be trusted out of hand).
Otherwise the two most common issues are EMF interference and not enough well working Zigbee Router devices with good reception close to devices with issues, so suggest take active actions to avoid sources of EMF very close Zigbee devices (especially for the Zigbee Coordinator adapter) as well as add a few “known good” dedicated Zigbee Router devices.
I highly recommend reading and following all the tips here before even trying to troubleshoot any deeper to rule out those well known issues → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage