Suppose you sent a secure message to a contact. The contact moved it to a folder "2020". This move will show on your side too. However, suppose you wanted to move the message to a folder named "Bookkeeping".
If you and the contact do not agree on where a message should be placed, the easiest way to solve the problem is forward that message to the contact again - this will create a new copy of that message at the top level contact folder. Now you can move that new copy to the subfolder of your choice (while the original copy stays in the subfolder where the contact wanted it).