I've sometimes seen icy formations form and break off of spacecraft. In today's SpaceX launch, there are a couple examples (times based on video) at 51:55 where you can see it growing:

Two similar structures are visible at 49:53 (you can see the larger one break off and more gas or something escape a few seconds later), helping clarify:

or at 50:26, which seems to be on the other side:

My best guess is that this is frozen propellant for whatever small thrusters keep the rocket on course, though the first time I saw the first example it seemed like something leaking out of the large ring. If that's it, does this icing cap/clog the thruster and make it less effective, or risk cutting off the course correction capability altogether?