I see the rotation is very jerky but only lasts about 1 second. How many frames is the animation for the rotation? What is your frame rate set to?
Okay - I think I found a way - I rotated the asset more than what you had and it looks much smoother. I think there's some kind of delicate balance between frame rate, number of frames and the distance an asset is rotated when it comes to how smooth the animation will be.
Download my FLA
Your bitmaps are very large in both dimensions and file size.
Also you're using a very short rotation.
If you change this you're gonna probably see a performance improvement.
Plain and simple: Flash / Animate cannot Classic / Motion tween small rotations over longer spans of frames.
This has been a known issue for decades.
In your case you have 0° to -3.5° spanned over 50 frames.
If you use classic tween instead and convert all frames to keyframes you can check the rotation values for each frame and it all will become quite obvious.
You can try manually setting values such as -0.1° or -0.2° and you'll see that they get rounded to zero.
Flash just can't do this kind of thing.
It has nothing to do with your frame rate or the size of bitmaps as the ACPs have suggested. Even if you had just a vector rectangle you would face the same problem.
The problem is mathematical and how Flash rounds and calculates rotations. -3.5° over 50 frames just does not give it enogh increments to work with and that is why you end up with a jerky movement that is literally one step every 6 frames or so.
This smooth rotation just cannot be done with a Classic or Motion tween.
Now here is what you CAN do: You break apart the bitmap and then Shape Tween it inside your container.
Shape Tweens don't have this problem and everything works as smoothly as you need it.
Here is your fixed file: https://drive.google.com/file/d/1aNKS6FSYldy-aIxek9-_a7qekxvf5Vj7/view?usp=sharing
Very good answer!