This is expected behavior if the transport nodes are in different subnets and no gateway is configured in the IP pool.
Improvements have been introduced in VMware NSX 4.1.2 will alert that a gateway has not been added to the IP pool when preparing a transport node using an IP pool which does not have a gateway.
Workaround:
As a workaround, you can temporarily add a Gateway to the ESXi transport node using the
vSphere Networking guide.
For a permanent fix, add the gateway address to the IP Address Pool, then re-sync the transport nodes so that the host configuration is updated.
POST API used to resync the transport nodes:
POST /policy/api/v1/infra/sites/{site-id}/enforcement-points/{enforcementpoint-id}/host-transport-nodes/{host-transport-node-id}?action=resync_host_config
If the gateway address cannot be added to the IP Address Pool because it is in use, then the transport nodes using the IP Address Pool need to be un-prepared first.
Then the IP Address Pool can be edited to include the gateway address
Then prepare the transport nodes again with the updated IP Address Pool.