Ok. I can suggest one thing to make sure all the prefabs are in the right format for the new Unity release.
Switch to inspector debug mode, click on all your sprite animation prefabs in turn, and change one value in there, save assets, rinse and repeat. Make sure nothing is broken at that point.
Check in to version control, and make sure the prefabs have changed. If you have text serialization turned on you should be able to work out what has changed. Hopefully, nothing serious.