Could have been a channel switch activated by radar detection. I would imagine that would only likely be triggered by military aircraft passing over, but I have zero knowledge of that. How the Pro Box would currently handle that is anyone's guess.
You would probably need to carry out a reasonably long survey of DFS channels to see which channels may be affected & how often. I would imagine you would need to run a spectrum analysing type USB dongle with appropriate software to do that, or resort to trial & error.
But given how the standard channels are relatively uncongested, it's probably best to stay in that area, using a typical WiFi analyser to pick an uncongested channel.
