O365 Onedrive for business mapped drive issue

Dear Experts,

I have a small group of users with O365 accounts. All have access to a onedrive share to which I have mapped a drive letter.  This has worked well for over a year now.  A few days ago, one user approached me complaining that the mapped drive was disconnected. So I logged on to the portal, browsed to the share and opened it in explorer, then I could re-map the drive.  However, as soon as the computer restarts, the drive disconnects again.

So far, I have:
- checked website address exists in the trusted zones
- checked the webclient service is running
- cleared out all temp files, saved passwords, cookies and temporary internet files
- removed all entries in the windows credential manager
- changed the O365 password
- logged in checking "keep me signed in"

I have also tried mapping the drive from a command prompt.

I read somewhere that a token may have expired.  Can this be renewed?

Any suggestions

Many thanks