In the Baylan Skoll Event, Padawan Sabine doesn't lose Stun Immunity after using an ability on her turn.
The two screenshots attached show the moment point where Sabine gains the effect, as well as Sabine using her special ability and still having the immunity.
What's also important to mention is that Ahsoka Tano in the event can also gain Stun Immunity, but this effect does expire when she uses an ability on her turn. That leads me to believe Padawan Sabine's effect is not working as described.
