it’s just the difference between the actor tick, physics tick and possibly the tick of the character movement component. for instance, if you put the stop movement immediately node that i showed you on event tick without the gravity scale node, the character will very slowly fall down (slower than a feather) because of the small time gap between the physics tick and the actor’s event tick, but disabling gravity fixes that.
You’re adding an impulse opposing the current velocity, but you have to achieve that velocity before the impulse can be applied which means the character must first be moving in order for the counter impulse to be applied in the first place, it’s a bit of a catch 22 really. Unless you’re moving there is no impulse, and because of that you can move for whatever milliseconds there are between each frame.
The reason you are able to move with the impulse, but not with the stop movement immediately node is, if i were to guess, because the stop movement doesn’t just cancel velocity but also acceleration, which means any movement between frames would become too small to be humanly perceivable.
With your impulse, the character’s acceleration is probably still rising which will move the character by the acceleration between each impulse.