we are using Office 365 Pro Plus in the latest version on Windows 10 1709.
User tried to open a word document on a network drive. (Server is Windows Server 2012 R2 used as part of DFS). The user was informed that the document was open by user x. After investigating the document was opened by user Y. User X is not part of the appartment but is an administrator but not in charge of the filestructure or maintaning it.