It has happened, at least once. But, as it is widely publicized when it happens, I believe it is extremely rare, a "unicorn" event. I believe that CCW carriers are targeted much more frequently. I have posted several stories where CCW carriers were attacked and then had to access their concealed weapon.
If it is widely publicized, then how come I've never heard of it happening anywhere, ever?
I was OC in Phoenix because I didn't have an AZ-recognized CCW, and the sketchy guy who was making a beeline for me from across the street at 10pm acted like he hit a brick wall when the streetlight reflected from my pistol, and hurried off in the opposite direction.
Most criminals aren't swaggering thugs, they're just looking to get as much as possible with as little fuss and effort as possible, and attacking someone you know to be carrying a gun is the OPPOSITE of little fuss and effort, and so that people have this idea that open carry invites attack is just downright weird to me.