Hi Nicole!
Thanks for sharing that screen recording! Sorry to hear you are having issues getting your images to slide and crop properly!
I've recorded this Peek to show you the results when testing it out on my end.
I was not experiencing the lag issue we saw in your recording, however, I was able to reproduce the black borders occupying the blank space left after cropping an image.
I've opened a support case on your behalf so one of our support engineers can look into this further for you. They should be in touch shortly!
Please let me know if you have any more questions!