Satellite issues

The base and satellite are about 30 feet apart, straight shot, on the same floor.  Construction is studs and drywall; no lathe or wire mesh in the walls.  The house is about 1500 square feet in all, but I’m five feet from the satellite so that’s not an issue. I’ve already disabled most of what you suggest to no avail, but will try moving 20/40 to 40. I’ve of course done full system resets - cable modem and base as well as the Orbi.  

2.4GHz is set to auto but the test devices are all running on 5GHz which is set to channel 48; there are other networks in the area on 5GHz (3 altogether) and this is the only one running on channel 48.  (The other 2 are on 153, together, go figure.) The interference graph is clean whenever I check it, but I’ll try another channel anyway.  There are plenty of 2.4GHz networks walking on each other but that would not impact these tests.

I’ve kept this setup painfully simple - Orbi Satellite to Orbi Base to cable modem; no switches or other devices in between.  I also do not have the Circle filtering setup.

The key thing here - no issues in the living room, where I would connect to the base unit, only in the back of the house where I’m on the satellite.  I had the service provider out and they traded out the modem for a new model, tested it (getting something like 250Mbps or 300Mbps), and I tested it out there with nearly the same results (base unit).  The oddball thing is that it was working great for months then just suddenly started having all kinds of quality/performance issues.