We needs to connect two 515 with mesh, managed by central and with an LTE(USB) uplink only. So, one AP will be connected with the USB modem and the other AP will have only the mesh link.
This scenario is working for us only when we have an ethernet uplink. When we remove the ethernet to have the USB Uplink only the second AP get out of the cluster. The AP with the Uplink stay working fine, but the AP that have mesh only do not enter the IAP cluster and do not broadcast SSID.
In this scenario the mesh link works fine, I mean that the mesh portal and mesh point can establish mesh successfully, but do not enter on the cluster.
This print shows the mesh working fine but only the AP with Uplink connected on the cluster.