What this tells me is that somehow the MS Teams application is also managing check outs. Once I had it open in Word, I went to 'File > Info > Manage Document', cycled through Check out and Check In successfully. Use the option 'Open in Word' and not 'Open in Word Online' or 'Open in SharePoint'. The fix in my case was to confirm I was unable to make changes from within SharePoint and then go back to Teams. I had assumed that Teams was a collaboration tool layered on to SharePoint and that somehow SharePoint would have ultimate control over the file pemissions.

As mentioned, I am in an working environment of SharePoint / Teams. To reiterate from before, I received messages that somehow the system thought I was personally responsible for the lock out and I was unable to control this file.

I'll be watching this thread for solutions. I remember this sort of problem back in the days of SP 2003 and SharePoint Designer was a big help in those days, sure do wish we still had that. Oh, and I have tried resolving this in both Teams and SharePoint itself. MS Teams is overlayed on SharePoint, the MS Upload Center has run a few times and the cache is clear. I have resorted to downloading an offline copy to do my work. The funny thing is the user that locked it is me! I cannot edit, save, delete or anything. I now have a locked file (Word DOCX) that has remained locked for a few day.

How to lock a folder mac