Xcel via a COM DLL challnege

Question

We have a product that provides data asynchronously to Excel, via a COM DLL. This works for Office 2016 (DCOM authenticate on Excel = connect), but not when changing to Office 365; unless the authentication level set to None I have created slides to illustrate this. I would like to know why this is. When did it begin and how often does it occur? Changing O2016 => O365 What errors do you see? Access denied when using O365 What's the environment and are there recent changes? As above What have you tried to troubleshoot this? Changing DCOM for O365