We are trying to grab post level information for Facebook Insights.
Until a week back, we could grab historic data for post level. However, we can't grab this data anymore.
You are most likely suffering from the same bug in Facebook Insights API as everyone using it (not related to Supermetrics). Facebooks development team is aware of the bug and are working on it. Unfortunately all we can do now is wait for them to fix this issue.
If there's anything else that we could do for you, please let us know.