Today on Ride of Steel the chain "broke" according to WVEC. I have never heard of this happening. The anti rollbacks caught the train and everyone was evacuated off the ride.
All the Intamin Superman: Ride of Steel coasters have had chain problems in the past. SFNE had issues with theirs during the first few years of operation and SFA broke two chains in its opening season. Darien Lake has had one broken as well.
Chain breaks happen quite often but they mostly go unreported. Most coasters go through about 2-3 sets of chain a year depending on all sorts of things like weather, weight and durability.
There was one year I believe Scream Machine at Great Adventure went through like 3 sets of chain in the course of a summer season.