Esri released a patch for ArcGIS Desktop, Server and Engine. It addresses an issue where calling the Buffer method on a polygon, which is created from a degenerate envelope, causes a failure. This patch is required for all 10.6.1 users and Esri recommends that you install this patch at your earliest opportunity. To apply this patch, please following instructions on
https://support.esri.com/en/download/7636.