problem is not with texturepacker but with unreal and how it manipulates data from texturepacker.
It is a little difficult to explain with words but let me try.Lets say that you have a jumping animation.your player starts from bottom center of your png.While he jumps his body is moving away from bottom and going up. changes size of png.If your player is 100px and jumps 500px then you end up with a last frame of 600px tall.correct?
Now if you want to keep your texture size small (2048x2048) for size and memory reasons (especially mobile) you need to crop 500px of white space so you can keep everything neat and tidy.problem lies in fact that your player until he reaches his maximum jump height he has to go through all sort of different Y numbers (height).He starts from Y=0 then next frame is Y=17 then Y=45 and so on until he reaches 500.Now with all those different png sizes Texture packer puts them in most efficient way possible inside a texture but that means random x and y coordinates for every frame.So if you want for any reason to offset something you are screwed! only solution to is if lets us input an offset that automatically is getting added to original coordinates. Trust me. i have more than 60 animations and a few thousand sprites currently in my game and it is a nightmare if you ever need to change anything with current system.