In some specific situations, you might see people having issues accessing shared files in the room. Guests, as they have very limited access, are not able to access any file that is not in the room they are currently at. This article will provide more information about this restriction.
Guests have very limited access to your office. They are not supposed to walk around and see all the available shared files in the space. That is the reason they can only see and access the shared files in the room they are currently at. Other shares are restricted for them.
To be able to give access to the file in the other office, you need to actually move the guest to that office using the "Get ..." feature. This will allow the guest to see the shares in the new office, but will restrict the files in the previous one.