To my knowledge, Augustin didn't really do all that much, so part of me thinks they may have removed him from office, but they would have hesitated to kill him, if only because it would seem too much like the bad blood (guilt through blood relation) they criticized Robespierre of beginning to lean toward. Still, in a panicked situation, principles tend to go out the window, so they might have just seen something named "Robespierre" and viewed it as a danger.