Not a biggie but I can’t get rid of this gap, moving the scroller around doesn’t erase it. Not sure the steps that created it, nothing special other than I think that was the original drop size of the second region. Oh one thing, I switched from 3/4 to 4/4 time to match the GA pattern I was looking at, that might have done it somehow.
Interestingly, I tried to set the TS to 2/4, and prolonged the midi trigger region, and the gap seems to be every 5 bar (excerpt the firs 4 bars) even if I put it back to 4/4: every 5 bars a gap (only in Galley view):
Try not to get too hung up on these kinds of things in galley view. Dorico splits the endless system into smaller chunks and processes them individually. You should only worry about a graphical infelicity if it shows up in page view, and even then, I’d probably only really be inclined to worry about something that is intended to actually print.