It could be anything from a dead or hot pixel (although it looks like too many that would have been caught in QA/QC), to dust on the lens inside that is giving that effect, to IR reflection from something else, to NR algorithm misinterpreting what it sees and leaves the pixel on instead of "dancing" off and on.
You could try adjusting sharpness and NR to see if you are right on the threshold of a value that is keeping those on if that were the case or to minimize you seeing them.
In any event, it isn't something that would negatively impact the performance of the camera and you could still make a good ID if someone came through.
Usually IR reflection is more pronounced, so I do not think it is that unless you are in a climate with moisture/dew that is reflecting back these tiny dots or location with lots of little reflective bugs that could mimic this, or even metallic in the fence, paint, or dirt. I am leaning towards your settings are just on the threshold that it is sending mixed signals to those pixels. I just don't think that many would have made it past QA/QC.
Something I have done in the past when I had "stuck" pixels was take a white sheet of paper and take it all the way up to the camera so that the entire screen turns white due to the IR and hold it there for a few seconds. Sometimes "flooding" the sensor with an all on pixel command can get them going.
