I don’t think this has been reported yet, but the randomize start position function in the Playback Options in Dorico 4 does not seem to be working, at least not for me. I set it to 100% and the notes are still stuck exactly to the grid lines. I went back to v.3.5 and could see that the notes were randomized with the same setting.
Is it possible you are looking at the “Notated Durations” rather than “Played Durations” mode in the key editor? In v4 this is now the default view.
Actually yes, you may well be right! I do apologize. I’m not in front of my computer right now so can’t check, but I’m sure you’re right. Thank you.