The auto save function in Office 365 will only work when files are stored on OneDrive or another SharePoint area, like Teams. Files that are saved locally or on NMBU network disks like Y or W will not auto save.

It is therefore important to remember to save manually when working outside of OneDrive/SharePoint. For more info about this read here:

https://support.office.com/en-us/article/what-is-autosave-6d6bd723-ebfd-4e40-b5f6-ae6e8088f7a5