These higher hits aren't all created equal and there are several reasons they can happen with the most obvious being an early elbow drop. But this is def possible without an elbow drop!
As one example, for players that have a bit of a dip to their stroke due to how the cue pivots in their loose hand, it is quite common to hit higher than they cue up. That dip makes them cue up lower on the shorter warmup strokes but occurs later on in the full stroke causing the same feel, with a stable elbow, to hit higher than they appeared to cue up to the ball. It's not that the tip comes up off the plane it started on (tho some def do like the elbow droppers), it's that it stays on its straight path longer before dipping to the cloth.
Really, just the very loose clasp on the cue, combined with the decel of the warmup stroke before the cb, makes the tip dip below the level that the stroke would go through on if it kept accelerating. So, when the final stroke is delivered, it comes through higher than where it dipped to on the warmup.