Since bugs can be present for years, it could very well be that a fix somewhere in your specific situation triggered a failure that made the system hang. Since there is no specific culprit to identify except that is happens in your situation, provide some system logging and your active extensions.
List active extensions:
$ gsettings get org.gnome.shell enabled-extensions | tr "," "\n" |tr -d "^ ' [ ] " | sort
errors in the journal from current session:
$ journalctl --boot -0 --priority=err