Hello.

So, it is the same user on both instances, right? Then the last done changes are saved. So, when both users are editing and both save document, the second save override the first one. So it is expected result. If you want to avoid this situation, you can use own account for every user (content editors) and then use check-in / check-out feature, so when one user is editing a content, no one else can edit it too.

Best Regards,
Radek Macalik
Support Engineer