Trimmed animation breaking on reload of Unreal

when taking a character like ParagonLtBelica if i copy one of her animation files, Rename the file, then trim the file to removes some frames it will work and show the correct new frames working until i save and close unreal. when i restart unreal the next time the animation will be the same number of frames as the trimmed should be (example 11 frames) however the animation does not play. its as thought its frozen on one frame.