We have had this kind of problem at the beginnig of our collaboration. The cause we found were three:
The oxide is too aggressive and go on to work also after polishing of the first layer of silver
The process of polishing and cleaning of the surface after oxide is too soft
The waiting time is too long from the oxide at the final polishing, In Vicenza, in winter, one night is not a problem but in summer 3/4 hours could be a problem!
In the pictures I have noted the colour of the oxide is a real dark black, so I think the first dot (1) could be the reason.”