Zigbee is very sensitive to interference and has a very short range so it depends on you building a good Zigbee network mesh, thus the root cause is almost always a combination of interference and users adding too few good Zigbee Router devices from the beginning (quick tip is that should be to start with adding a few mains-powered you know are good Zigbee Router devices before adding any battery-powered devices). Highly recommend that you read and try to follow all these best practices → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage
If some devices after do pair/join successfully but do not show all entities (features/functions) that are expected then you likely need to submit a device support request to the developers of the Zigbee solution as that specific device may be using non-standard Zigbee clusters and/or attributes which will then need to be translated and coded into a code library for device handlers/converters, for ZHA see docs → https://www.home-assistant.io/integrations/zha#how-to-add-support-for-new-and-unsupported-devices