Before troubleshooting any deeper be sure to first upgrade the ConBee firmware:
https://github.com/dresden-elektronik/deconz-rest-plugin/wiki/Update-deCONZ-manually
https://deconz.dresden-elektronik.de/deconz-firmware/?C=M;O=D
https://flemmingss.com/how-to-update-conbee-conbee-ii-firmware-in-windows-10/
Also highly recommend take actions to avoid EMF interference as well add some known good Zigbee Router devices before troubleshooting any deeper as both of those are known to cause weird and intermittent issues, so read and try to follow the tips here → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage
You can as a last resort upgrade the firmware on the IKEA Zigbee devices but that is generally not needed or recommended to do on all devices unless having issues that can not be solved in other ways → https://www.home-assistant.io/integrations/zha#ota-firmware-updates
If you have already upgraded ConBee firmware and also taken actions to avoid EMF interference as well add some known good Zigbee Router devices then actually suggest reporting the issue with debug logs to home assistant core repository before upgrading IKEA device firmware → https://www.home-assistant.io/integrations/zha#reporting-issues