What kind of strap or bracelet are you using? Do you have a ring on your watch hand?
If you are putting your hand through a bracelet or closed strap, and the opening is tight, the bottom of your watch can catch on a ring.
The surface of SS is soft and easily scratched. Sapphire is much harder, so you would need a very hard ring. Like tungsten. Or a ring with a diamond in it?
Sapphire, while one of the hardest materials, can shatter or chip. Diamond is harder than sapphire.
Until fairly recently, many dive watches, even some of the most iconic pieces by Rolex and Omega, used various forms of plexiglass rather than sapphire. The reason is under pressure, a hit that could glance plexiglass, perhaps leaving a scratch, or worst case a crack, could shatter sapphire. If the sapphire shattered, the seawater would almost always ruin the watch. But that was less of a concern: the diver would not be able to time the rest of their dive. That could be life threatening, depending on the circumstances. A cracked plexiglass might not be deep enough to let water in, and the diver had a better chance. And plexiglass was cheaply and easily replaced.
All of my regular watches on bracelets develop, over time, a series of small scratches, at what looks like a similar angle to where your chip seems to be. About 6 or 7 years ago I lost my 26 year old, very beat up, gold wedding ring. I decided to replace it with something more durable: tungsten steel. I noticed my watch case backs getting more significant and deeper scratches. I'm always careful now when putting on watches to avoid the ring.
Just a thought.
