First of all, you should not use any assets minification plugin as the theme itself minifies its assets and having those plugins will make the assets double minify which will stop the normal functionality.
I checked the case with my local installation with version 5.1.1 and the One Page Navigation functionality is working correctly. Kindly start over the settings with the guide below:
Also, kindly check for 3rd party plugin conflicts if you use any.
Hope it helps.