Yesterday, I finally grounded both the guy wire and the DSM. However, I forgot that I had noticed the DSM being down and staying down the day before. Thus, the DSM stayed down all day. The Ubiquiti was up and connected, according to the LEDs. I also yesterday noticed an issue when I couldn't ping anything on our Marshall wifi network for an hour or so in the afternoon. This problem went away later on.
This morning, I found the console port on the Pi to be unresponsive, so I did a power reboot to the DSM. Everything seemed to come up okay, and we are getting ncharts data again.
As an additional precaution, I adjusted the Ubiquiti azimuth to point east of the station adaptor, to give it more beam separation from SPol. I still had the full (4?) LED signal strength indicator. With a ~30-degree half beam width for the NanoBeam, it still will see some SPol signal.
SPol ran briefly (one complete scan) while I was there and the DSM stayed up, but I don't know if SPol was transmitting. We'll keep monitoring...