Cannot log in to Portal for ArcGIS 10.3.1 from Esri Maps for Office 3.1 in PowerPoint 2013 (32 bit) when Portal for ArcGIS is using Public Key Infrastructure (PKI) authentication.
There are multiple reasons for this bug to occur. This issue will not occur in the next version of Maps for Office and will implement newer technologies similar to the technology used for Esri Maps for Office 3.1 in Microsoft Excel.