i4 owner ~850 miles. I've noticed this 3-5 times, but I feel like I've learned to upshift sooner or be stronger on the throttle. It's like you're walking the line between the car wanting to stay in lower gear and be aggressive when not pressing the throttle enough. Causes the car to slow from the engine just enough to push you forward in your seat, causing you to hit the throttle slightly, bringing speed and revs back up, causing you to go back slightly, repeat. I feel like since I've changed my driving habits slightly it doesn't occur much.