Turns out the button on the top of my RTL510 had gotten soggy over time and the unit was turning off and turning on in a cycle.
Replacement arriving today.
I was able to clean it out, and I guess you have to clean the area from time to time.
If your Varia radar power button doesn't have good pushback when you press the power button, time to clean it up with warm soap and water and a toothbrush until the power button comes back to life. Happened so slowly over time that I didn't notice.
