We can't know. You have not provided any details about the layers. Typically this can happen when you use time-stretching/ time-remapping, but it's realyl not clear what you do.
I have not used time-stretching / time-remapping, these layers are compositions.
And within these compositions, the layers are normal how much the frames in the timeline.
Thank U! Only now I understand, it happened to these layers, because when they were created, the main composition was 59.94fps, when I change to 29.97, they are staying in the middle.