Using version 18.104.22.168 and the User Preferences option to "Show Dashboard at Startup" is not working. Users have this selection checked but no Dashboard is visible. They have to do CTRL+F12 or click on the dashboard for it to show up.
With the release of 9.7.1 there was a global option defined for showing the Dashboard as a Feature Request. By default it is unchecked. To force the use of visible or not visible for the Dashboard through User Preferences: