Power BI report server with custom security save as issue

Have you tried debugging your custom authentication code while doing the save as operation? I just had someone on this other thread https://community.powerbi.com/t5/Report-Server/Unexpected-Error-Power-BI-report-Server-With-Desktop-While/m-p/943361#M13161 say that they found and fixed an issue with custom auth and the the Power BI Desktop "save as" dialog. (unfortunately they did not provide specific details and it looks like they've deleted their forum account so there is no way to contact them)