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. The Ubiquiti was up and connected, according to the LEDs.
This morning, I found the console port on the Pi to be unresponsive, so I did a power reboot to the DSM. Everything seems okay.
As an additional precaution, I adjusted the Ubiquiti azimuth to point east of the station adaptor, to give it more beam separation from SPol.
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...