Task ID’s are all in the correct order. It just seems to have completely changed all tasks order. When i open the file it has dozens of circular references because it’s moved tasks from one place to another, and indented tasks in a seemingly random way.
I tried on two other colleagues machines, emailed the file, saved on C drive instead of server, with the same result. I then tried on another colleagues machine and it worked without problem. (only difference is that her machine is a bit older) Trying a repair/reinstall of microsoft office now to see if that fixes it.