I would expect that 99% of all those sightings are ice crystals flaking of various parts of the spacecraft after urine dumps, or from moisture that collected on the surface of the spacecraft as it sat on the pad waiting to be launched. The ones that appear to change direction are simply being hit by gas expelled by the reaction control jets when they fire. They are very small objects very close, not large object at a great distance.

The other 1% probably consist of loose objects left behind during launch prep. I remember when they were finished with a Mercury capsule they would put it in a jig with the open hatch down and shake it till things stopped falling out.