Sync Center is a feature in Windows which allows users to work in offline mode when there is no connection to the server share so it essentially keep copies of the network files locally on the PC. Once connection has been re-established to the server it will then synchronise the files.
To the unknowing users this will all be seemless until a problem arises with Sync Center where it suddenly stops synchronising the files. So any changes made by one user will not get updated to the network so other users will not see any changes.
If you use Sync Center then you will need to review the sync conflicts and resolve them.
If you don’t use Sync Center then you can disable offline files.
You will need to contact your IT if you require assistance with Sync Center.