Hi Scott,
Out of curiosity, are you performing this call anonymously or with a standard user account that is used for rest api? If so, some posts may be hidden if the user had made a post in a private area or had one of their posts moved to a deleted posts board (or something of that nature). This may not be the case, but I thought I'd mention it. If not, please feel free to open up a support ticket (Support Category - select the Cases tab) and we can retrieve further information and investigate what the problem might be.
Regards,
