So here is a MAJOR pet peeve with Dorico, and if I think I had a chance I would request a refund.
Here’s a scenario I’ve run into a few times. I finish a document, I get the layout how I want. I have a rehearsal or a gig, and realize I need to add a section or edit the document somehow. Once the engraving is set, if I add bars (for a coda for example), it causes MAJOR layout headaches.
Does anyone else have this problem?
Example attached:
From time to time vertical justification can kick in and, yes, it’s annoying.
I’m not sure why the distance between the last two systems shrinks but I’d say there’s a good reason. Can you upload your project with just this layout?
You probably moved the systems position manually, so that when you add more music, Dorico applies the automatic justification that collides with your manual adjustment.
In Engrave mode, select something in the frame/page, go to menu Engrave > Staff Spacing and choose Reset Selected Frames. Or, if this is not enough, choose Reset Layout. The automatic justification should take care of it.
Generally is suggested to let Dorico automatically adjust the systems, adjusting the global Layout Options > Vertical Spacing.
As Christian mentioned: if you achieved your layout by adjusting the layout options/settings, then you will be fine - even after adding new bars.
If on the other hand, you have achieved your layout by manually moving staves, you are out of luck. Dorico respects your overrides in a way, that it will not clear them - once you add new material. Once you have done manual overrides it stays your own responsibility.
It takes a while to understand this concept, but it is really quite logical.
Forget everything you might have learnt and got accustomed with in Finale. The only thing to keep is your creativity 
That is profoundly bad programming, in my opinion. I should be able to move anything any way I want, and add bars with no barrier to creativity.
In a simple page like that, you shouldn’t need to move much manually to start with.
Most problems in Dorico come from doing “too much”.