It's good your watch was under warranty and they repaired it. I find most manufacturers will never admit to any mistakes from my experience they will tell you what they fixed but never really get into the details or ant defects in their manufacture.
I have fixed a lot of watches for people where the screw holding the rotor backed out that seems to be the only common problem I have come across with autos. The rotor became loose of course, the screw jammed up the works so the watch could not be even wound manually and just stopped dead. There was only one I couldn't fix. You have to be careful not to get to aggressive with winding the watch when it stops like that. One of my friends trashed the movement on a fairly expensive watch trying to manually wind the watch with the screw logged between some gears. It ended up costing IMO more than the watch was worth to get it repaired. Some watches I fixed were new some were older. It shouldn't happen on a new watch. IMO it was just something over looked at the manufacturer. I do not know what the tolerances are for torque on watch screws or what tools that might even measure it.
I have fixed a lot of watches for people where the screw holding the rotor backed out that seems to be the only common problem I have come across with autos. The rotor became loose of course, the screw jammed up the works so the watch could not be even wound manually and just stopped dead. There was only one I couldn't fix. You have to be careful not to get to aggressive with winding the watch when it stops like that. One of my friends trashed the movement on a fairly expensive watch trying to manually wind the watch with the screw logged between some gears. It ended up costing IMO more than the watch was worth to get it repaired. Some watches I fixed were new some were older. It shouldn't happen on a new watch. IMO it was just something over looked at the manufacturer. I do not know what the tolerances are for torque on watch screws or what tools that might even measure it.
