I signed in with Microsoft and could vote just fine.
I also got a page that made me authorize my browser as having permission to access my MS data. Did you also get that screen? It might have signed you out due to lack of access authorization.
I too granted permission and even got the email confirming that I did such. Sure needs a lot of access to just vote. I gave up as I am not sure what the issue is. Maybe due to traveling right now.