In a sort of butterfly-effect turn of events, it was because of bar 42: you had added the arpeggiated left-hand chord on the last quaver beat, when it should be on the 3rd crotchet beat (ie a quaver earlier).
Moving that chord back a quaver allows an extra bar to fit on that system, and the rest of the piece flows from there.
You’ve also got a double slur in bar 43.
PS there have been a couple of Dorico updates since 5.1.50, most recently 5.1.70 earlier today.