This was in 2.3.1.1.
I clicked the edit option on the workspaces tree. I then changed the name, the located under, and in this particular case, I believe, I did something I don't normally do - I removed permission for myself in error, and then re-added full permissions prior to clicking save.
Somehow this resulted in the file not being accessible to me, but still to the other users.
If I re-subscribed to the file, it became visable again to me.