Good evening Matt.
The plot thickens!
So I found another post where someone was having a similar 20Mbps download speed on mesh, and one of the things towards the end that they tried was making an entirely new SSID, and then switching over to that new one. I created the new SSID, but without “WPA3” checked, and lo and behold, fast speeds. I then switched back over to one of my original SSIDs and I’m still getting the faster speeds. It may not be quite as fast as just the one node, but now the downstairs devices have better connections. So I do feel there’s a bug somewhere in there (memory corruption?), but am happy to have found a workaround.
If I wanted to try a manual Tx speed somewhere in between medium and high, what would you suggest? What would be the numbers for medium vs high? I imagine this would let the devices run a bit cooler.
Update: And just like that, I tinkered with a few settings and now I’m back down to the 20 Mbps rate. I changed the 5GHz channel from 149 to Auto for both nodes.