One RBS750 satellite very slow, shows connection as "wired."

I have an RBR750 with three satellites. One is giving me problems.
Symptoms are: single-digit mbps on Speedtests for all devices connected to that satellite.
Speeds are the same whether devices are connected to the satellite wired or wirelessly.
On Orbi router “connected devices” list, the satellite shows as connected via Ethernet. Other two show correctly that they are connected via 5GHz WiFi.
Devices in the room with the satellite show much better performance when the satellite is unplugged, at which point devices in the room (iPhone, appleTv 4K) are camping directly onto router.
I have rebooted the satellite and the router and the cable modem and the relevant devices.

I have tried swapping its position with one of the other two satellites--it still shows as "wired," even when placed in the same position as one of the other satellites.

 I upgraded to a three satellite system in large part to address the speeds in this room, so needless to say this is a little frustrating.
Does anyone have any suggestions? Thanks in advance.