Only some live photos turn into animated stickers

I can't figure this out, and it seems other people have had the issue as well but no solution. Some of my live photos turn into animated stickers when I long press the subject. Others won't. They'll turn into a static sticker. It doesn't make sense why some work and others don't. Some that work have complicated backgrounds, unclear subjects, and movement in the camera, but then others with clear subjects, centered and stable framing, and of different lengths, short or long, won't keep the animation. I don't understand what causes some to work and not others. Any solutions?