Console.app is located in
Please open it. In the sidebar on the left side. There should be "system.log" and various other logs. Interesting might be "System Reports" where you could find spin dumps, for recent apps which ended in "infinite" loop. There might be Finder_something.spin. That file would help us diagnose the issue.
Also in the "Devices" section there could be some recent problems...
Unfortunately troubleshooting problems during shutdown is tricky. You could also try to just log-off and log back in. Maybe you will be able to reproduce the same problem without rebooting.