There is a conflict with PowerPoint (and maybe some other office programs) and Google FIle Stream.  An option in file stream allows for seeing who else is editing a document, and this is not supported in office 2016, apparently.  The option is listed in the FS options as "Real time presence in Microsoft Office".  This can be un-checked individually on each user's FS settings.

Also, this option can be disabled in the Google admin console (and we've done so, but don't have feedback yet if it fixed the issue).

As a workaround, in office, clicking the "enable editing" button usually lets things work normally.  Usually errors messages are appearing and have to be closed with the escape key so that the user can click "enable editing" between error messages.