I don't know enough about you to speculate on why it's happening to you specifically, but a lot of factors can increase a disfluency, such as stress or anxiety or insecurity. For what it's worth, I think it's great that you're challenging yourself instead of just altogether avoiding your stutter, but you should also appreciate that the stress of forcing yourself to confront it so often (and with added pressure, since it's your job) is prone to stoking anxiety, which can then make the influencies worse. This is kind of circular, because logically, you'd confront the source of your anxiety to rid yourself of it, but many stutterers consider their influencies the source of their anxiety. To be honest, that's something most stutterers (me included) struggle with, and will continue to struggle with for most of their lives.