Client Credentials REST Host 403 after 1 hour

I'm in the process of migrating our old forum threads/replies into a new community instance using the ClientCredentialsRestHost PostToDynamic method and find that after 1 hour, the API response is "The remote server returned an error: (403) Forbidden".  It happily chugs along, creating away until an hour passes. The documentation seems to imply that the host will handle getting refresh tokens. Maybe i've missed something in a configuration or a setting that extends beyond the hour limit.

Can anyone help?