Look at this document: https://docs.hubitat.com/index.php?title=How_to_Build_a_Solid_Zigbee_Mesh
Yes, Zigbee devices must be paired in place. If you cannot pair in place, then your mesh lacks sufficient powered repeaters, and that device will not work where you have it.
A Zigbee mesh network will generally self-heal if you shutdown the hub for 20 minutes, and then start it up again. This self healing process can take 24 hours.
