Hi,
Have you checked the status of the network drive? If there are no issues, try to disable/re-enable the offline files and see if it resolves your concern.
Also, check if there's a group policy the allows or disallows the "Enable Offline files" feature. On the Run box, type rsop.msc and see the policies under Computer(User) Configuration/policies/Administrative Template/Network/Offline files.
You should also check if there are sync conflicts in the Sync Center. If the issue persists, try to set up a new sync partnership for your offline files and check the results.
Thanks.