yes, this can sometimes happen because there is not a keyframe entered for every frame and our animation system does not run from frames but rather is based on time, so if there is no entry at said point, then the frame will not be registered and consequently not displayed in the timeline.
This is caused by some exporters creating optimized key frames where they interpolate over time rather than having an entry set in stone essentially.
What you can do is try to re-export the FBX file and this time choose to have a keyframe per frame to ensure skyline will pick up on it. When max is booted i will have a look at the settings for you.
I htink the other option you can choose is baking the animation to the file.
Hope this helps