I’ve had a similar issue and can’t find documentation on this anywhere.
Recently the box that appears when insert/edit link button is pressed in visual editor the dialog box just displays the home page of my site instead of the options for inserting or editing a link.
Can still add link in html view but my clients who manage this site have very limited ability with html. It worked fine for a few months before thiss.
I’ve tried deactivating all of the plugins which made no difference.
Have updated to 2.8.4 and swapped themes, tried different browsers, cleared cache and cookies.