I tried your suggestion, disconnected repeater and reconnected, same result. I rebooted my primary wireless router, and rebooted the GL-AR750S, still sends the name as "GL-AR750S as the client ID. Here is a screenshot of primary wireless router’s dhcp lease pool, a Netgear NightHawk 9600;

I am pretty sure the Netgear is not the issue, as I have a TP-Link travel router that performs this same function, and what ever name I assign the TP-Link repeater shows up on the Netgear.

Not sure if this matters, but all my GL-AR750s clients connect on 5GHZ, the 2.4GHZ radio is only being used to connect the GL-AR750s to the Netgear in repeater mode.