Us old farts that have been in the industry for 30 or 50 years have seen it.
Its common to hand soldered items. You have to be looking for it.... Solder
with internal flux can often spatter. It happens more so with some fluxes
and a hotter [than needed] irons as the flux heats up and goes from solid
to gas and the solder with it. That sputter can end up everywhere and
anywhere. That with modern tight lead spacing and traces close to each
other often shows as hairline shorts. Little heat or solvent often breaks
This is less common with wave soldering, radiant heating, and IR heated SMT
soldering systems as there is less solder and the flux is not inside it. That
added to the thermal ramp to heating and cooling tends to avoid this.
Please reply on list so we can share.
Off list email goes to trash, I had to due to scrapers.