I would definitely like to test out some stuff if I had more time.
Your replay was made with 4.82 and duck's with 4.8 so it might be related to this set of versions.

These are the shittiest weeks of my year in terms of work though, so other solutions will have to wait unfortunately.

You can try running your replay through this http://toribash.enikesha.net/ , and remaking it exactly joint by joint with it, to see if the same happens.
Other than that for now, I can only advise you to make more saves when you're replay-making, and if it ever happens again post it here if you can. Maybe we can find out the pattern of the bug.