Just to share, maybe the staff can comment on that.
I guess the 'stop motion' animation is not really compatible with annotations, yet the annotation menu is available in the 3D settings so I used it with my simple animation.
In this first example (35 OBJ files), you can see that the annotations are not following the models which is probably kind of expected (but too sad !) since the frames are from different files, unlike a real animation coming directly from a Blender file (or FBX file ?) for instance.
Here comes the strange behaviour : in this longer version (50 OBJ files), the 3 annotations are all coming quickly to the center of the scene (behind the ball) after about 0.2 sec.
On a more general point of view it would be nice to have a timeline for the annotations, because you don't necesseraly want to have all annotations visible during the whole animation, even with a real animation file.
Just my 2 cents.