There is a known issue with Office 2016 for Windows, when switching from the protected view into editing mode. Microsoft Office falsely detects file changes on the server and attempts to merge local changes with server changes. After discarding a check out, Office does not reload the file from the server and still displays the version of the file that has just been discarded.
We recommend that you turn off the protected view, by adding your server in the trusted sites or local intranet zone, or alternatively by deactivating the protected view in Office. You can deactivate the protected view by selecting Options, and Word Options, then Trust Center. Select Trust Center Settings and Protected View, and deactivate all settings. Save your changes.