box is adding new files instead of updating my file. Why? How to make it stop?

My company started me on "box" about two weeks ago. It has been OK. But as of this afternoon, one of the main files I work with is not being updated. I have it stored in box. I open it from there. I work on it. But when I save it, box creates a new file instead of updating the original. I now have several files with names like "my file (my.email@my.company 5) .docx" Why is this happening? How do I get the standard behavior back? FWIW, I am working from a Windows 10 machine.