@Ogabeg to me it looks like there is a workflow if your users have to approve or reject an expense report, i could be wrong though, but from your description it almost looks like a Lock Record action in the rejected state of a workflow. We had a similar issue recently with some vendor bills that were rejected that our AP team could not edit after being rejected. Once we added their role to the condition to excluded them from the lock record they were able to edit them. Don't know if it is a similar issue with you, unless your approvals are done via suitescript