I just wanted to let the community know that every so often members of my team, including myself, find that the "Sign in" button (used to connect to AGO via the ADD Data button) becomes unresponsive.
We found that deleting the ApplicationSettings.json found at the windows path below fixes this issue:
C:\Users\[USERNAME]\AppData\Local\ESRI\ArcGIS for AutoCAD\400\
Not sure what the best way is to report this bug to ESRI-perhaps someone from the ESRI team can create a ticket?
Thanks, Jay