I had this issue for a long time that was doing my head in. The smooth scroll functionality was not working on my Windows 10 computer on Firefox, Chrome and Opera but it was working fine on Microsoft Edge, Blisk browser, my mobile phone and other computers! The problem was that the smooth scroll library GeneratePress uses respects the Reduce Motion setting available in certain operating systems. In browsers that honor that setting, Smooth Scroll will not run and will revert to the default “jump to location” anchor link behavior.
All you have to do is activate the option on Windows 10: Settings > Ease of Access > Display > Show animations. Problem solved!