This has happened with multiple animations before and I always wondered what is happening and why the easing of a curve is not smooth enough. Then I realized that the sequencer it itself is not applying the easing, as shown below. I tested in a new island and I couldn’t replicate, so my guess is that quarternion interpolation is affecting the movement here (I have it enabled) and because its two different curves, the easing doesn’t apply.
EDIT: It was quarternion after all. I think the bug is that quarternion overrides curve editor curves, making everything linear.