When I return to a project the binder icons for text files that chance based on the presence of text or synopsis text return to a blank icon even though text is present. Once I click on the file in the Binder it returns to the correct icon. The next time I return to the project, however, the same problem exists.
It sounds like your search index might be jammed and refusing to save updates (we use that to fill in the icons as that is way faster than checking the disk). Please reset it using the Tools menu from the project window, reload the project and see if that resolves the issue.
Are you working with the project in a sync folder such as Dropbox or transferring between Mac and Windows? If the problem is regularly recurring after using Tools > Save and Rebuild Search Indexes, it might be that the project isn’t always syncing completely between closing on one computer and opening on the other.