I bet Oregon Engineer would like to get his hands on that chain and do a Brinell hardness test on those drive links. That is not a brittle fracture. There is a lot of distortion but do I see some abnormal wear on the front of the drive tang just above the drive link scraper scallop about the 5 oclock position of where the rivet hole should be in the drive link? From the look of the top cutter plate two teeth back, you hit embedded metal but where the force came from to open the link like that is a mystery unless it was dead soft and missed the heat treatment. I would definitely try to contact Oregon technical people. You could always suggest that otherwise, you are quite sure Stihl will trade a new chain of theirs, just to have a look at that one, Lol! I would have some fun with that one: Just make sure there is no problem with your sprocket. Examine the rest of the drive links for any sign of localised wear on the drive links where the fracture originated in that link.