This may occur when NSX enabled clusters are configured in folders as opposed to directly under DataCenters in vCenter. The folder acts as an intermediate level between datacenters and clusters in vCenter Server.
When vRA collects transport zone information, NSX returns the scope (i.e., the parent) of each cluster the Transport Zone is connected to.
When the NSX clusters are configured in folders, NSX returns the folder id while vRA expects a datacenter id which results in vRA being unable to determine which clusters the Transport Zone is connected to.
Resolution
This issue is resolved in VMware vRealize Automation 7.4, available at VMware Downloads.
Workaround: To workaround this issue, NSX enabled clusters need to be moved from the folders up to the datacenter level.