There has been an identified issue with the Facebook Graph API that can lead to these errors in Supermetrics Queries for Facebook Posts:
FB post fetching error: Unsupported get request due to known issue with the Facebook Graph API. See <link to article> for more information.
FB post fetching error: Unsupported get request. (Supermetrics request ID: xxxxx).
The issue arises due to a bug with the pagination - if the part of the query needs to fetch more than 100 items, it will fail to get the last page of data and throw the "unsupported get request" error. This issue has been reported to Facebook and their developer team is investigating it for repair. See: https://developers.facebook.com/bugs/370983243719414/
You may be able to get around the issue by pulling smaller chunks of data for the problem period so that it is less than 100 items, but the permanent fix is awaiting Facebook's action to fix the bug. We apologize for the inconvience caused by this and we're hoping for a speedy resolution on Facebook's side to clear this error.