Near as most of us can tell, it's the trigger safety. Push the trigger forward too far and it catches on the frame.
Incidentally, I have a 2012 model as well, and I can only partially replicate the "lock up" as some seem to like to call it. To generate the issue by impacting the barrel you have to use far more force than anyone in their right mind would EVER put on the firearm (ball peen hammer at full swing, anyone?) at which point it is remotely possible to jar the FGC and cause the trigger to come forward and lock against the frame. Mine can easily be powered through by manipulating the slide, or the other option that takes even less effort is placing your index finger behind the trigger and gently pulling with your middle finger until the trigger disengages from the frame.