Broken world?

hey everyone, i haven't played minecraft in years but recently started again because of the confinement so ignore my old username! I started a new survival world and played for a while on it, without ever having issues. Since i started to get more invested in it, i decided to save a copy on a memory stick...just to be safe. I didn't change anything to the file, simply copied it. When i logged back on a bunch of chunks had been swapped, replaced or deleted. The copied world was exactly the same, entire chunks deleted and shifted. It can be fixed with a bit of time but i was just wondering if i did anything wrong? I'm just really confused as to what happened.
I would include a screenshot but i have no idea how to upload a picture of here