Hi, I have a little problem with arpeggios. The moment I want to move an arpeggio chord in the key editor slightly to the left or right, the “arpeggio effect” disappears, all notes then play at the same time. Is there a trick to move the notes without this happening (so that I don’t need to restore manually the arpeggio effect)? I tried to make a screen movie with OBS but unfortunately that didn’t work. The moment I move the notes in the key editor, the movie stops 
No, Dorico won’t apply the automatic arpeggio effect if you have adjusted the start or end offset of any of the notes. If you need to do that, you will also need to adjust the offset of each note to produce the desired arpeggio. (Dorico works this way so that your own recorded performance takes precedence over any automated playback effects.)