I may need a simple drawing as to your setup. Is the IAP inside, and is the IAP link running over the mesh or is the 175 outside and the client inside? If the backhaul for the speed test is over the mesh, that may be impaired.
With mesh, and if there is an SSID for clients on the 5Ghz then the mesh is split between the clients SSID on the radio.
Also want to make sure you are not associated to the 175 farther away.
So hard to tell here, may need more information to run this to ground.