Postgres 9.6.2 not stopping on Windows. Any idea?
Connect with psql and type this commmand

show log_destination;


this will display where logs are. If the output is EVENTLOG, then check Windows Event Viewer for any message from postgresql. I don't think log_destination is CSVLOG nor SYSLOG, so the last possible value is STDERR. In this case I don't think you may get the messages.
In order to change your configuration and use event log, see https://www.postgresql.org/docs/9.6/static/event-log-registration.html .

Once you know where the log is, check its content and you should be able to find the cause of your problem.