Unable to open files in Microsoft Excel Online

We have several excel files that multiple users need to be able to work in online simultaneously, but the files are only showing the option to open on desktop (no option to Open in Microsoft Excel Online).

So when people are saving their edits, different versions are being created of the file.  This is not happening to all excel files we have in Box, and some do have the option to open in either desktop or online.

How can we get back the option to work on files online?