A quick follow up, players have been discussing a similar issue in their MP game in the thread here: Bizarre glitches - the difference in their issue is it has happened for the host, not Player 2.
LeahW noted that if they reload 3-4 times everything usually rights itself. If you haven’t reloaded multiple times with your friend, and they are happy to give it a try, please do and let me know if it helps you at all.