The trick is to smoothly animate the filling of a random percentage of the remaining unfilled bar between, say, 30% and 70%, with the timing of the advancements

The trick is to smoothly animate the filling of a random percentage of the remaining unfilled bar between, say, 30% and 70%, with the timing of the advancements themselves slightly randomized. A sort of Zeno’s progress bar. It will neither peg at 100 nor shoot past, and the pulses feel “organic”. Bonus points for advancing the bar to known fixed points of progress when real feedback is received.