Is this site a multi ap site? Do you use frequency reuse? Is it only one ap/ direction or on multiple aps?
You do not need to be in a tdwr territory to get hits from a radar station. Weather radar can go a long way if conditions are right.
If it seams random then look at self interference. And signal that is not the cambium signal style can trigger the DFS mechanism and finding it can be a real PITA!
Try placing an SM in spectrum scanning and get some data. On one of my APs I was seeing a sudden rise in DFS hits and we ecentually found it was a TP Link 5GHz bridge that a guy setup without doing a scan and properly setting power levels. Set to 30dB and 60degree 13dB gain antennas for 400ft of path! An SM clamped on each side of the truck ladder frame allowed us to find several of these issues.
Not saying your havung the exact same issue, but happy hunting!