I was experiencing the same problem dropping my chain for no apparent reason, I attributed it to the fact that the front sprocket spins and sometimes just throws the chain off into the gap between the guard and sprocket. I solved the problem by having my LBS attach a plate on the inside of the guard to fill the gap, have not dropped the chain once since!I started to have the chain jumping out of the front sprocket. When it happened for the first time I have attributed it to chain slap as I leaned into the corner much and was on power pretty much right after. It got jammed between the sprocket and the chain guard and managed to chip chainstay a bit (it was a bummer, I didn't have chainstay skin). Since that I had the same thing happen again, which I again attributed to being in the highest gear, going fast and hitting some rough surface on the road. Today, it happened twice on the way to work, but the first time it was on the smooth road, chain in the middle of the cassette (no crazy chain angle etc)
I have no explanation for this except stretched chain. I have just over 1k miles on the bike and not something I was expecting to go weak in such a short time. When did you have to replace your chain and what type of riding do you do? I'm thinking about going with KMC chain, just not sure which one fits SC.
I'll attach a couple of pictures later.