RBS850 Poor backhaul status

I've got an Orbi RBR850 router and two RBS850 satellites. The router is on our main floor. The satellite upstairs (directly above the router) shows "good" for backhaul status, and was just added today. The satellite downstairs (pretty much directly below the router) shows "poor" for backhaul status, but has been operating with the router for ~6 months. (I just learned today of the web user interface...) Both satellites are connected via 5G and both have fully updated firmware. The 5GHz channel is set to 48. Apart from a computer (wired to the downstairs satellite) and peripherals, there are no electronics which I would expect to cause interference.  I'm leaning towards a physical reset on the back of that satellite, but welcome any other advice. 

After a two hour waste of time on the phone with Netgear CS, I'm hoping for input from people who know something... :)

Thanks in advance