Hello. Latest version 6.2.30
I don’t know if anyone has already encountered this problem. As seen in the video screenshot, simply adding text (in this case, to the violas) causes Dorico to compress the systems illogically. 
Go to Layout Options > Vertical Justification > Justify distance only between systems when frame is at least %% full. Adding that text item will have taken the vertical fullness just past this threshold. To avoid this, set the percentage higher.
Thanks! Higher or lower? 
Higher. Before you added that text, Dorico was justifying by adding space between both staves and systems. After you added the text, the frame fullness was over this threshold, so Dorico only added space between systems. You want to raise the threshold in order to counteract this.
Hi. Since there are no bugs involved in this thread, I modified its title with one superpower I was given some time ago (and try not to use too often).
You are absolutely right!
I don’t know. I’m sure you know better than I do, but when I increased the value, Dorico compressed almost all the systems in the score. The opposite happened when I set the value lower.
Perhaps it’s not clear what I want. I would like Dorico not to compress the systems.
Here is a page which is 64% full, no justification applied.
With Dorico’s default vertical justification settings (60% in the first box and 80% in the second box), Dorico adds space both between the two systems and between the staves in the systems.
If I lower the second value so that it’s less than 64%, Dorico only adds space between the two systems.
This is basically the same as the first image, except that the two systems have been spread apart by a lot of space. And I think this is what you want to avoid, right? The way to avoid that is to make sure that the second threshold in Vertical Justification is higher than the frame fullness, as it is for the second image.
Of course, different pages will have different fullnesses, and the vertical justification setting applies to all pages in the layout. If you don’t want Dorico ever to produce something like the third image, then set the second threshold to 100%.
Here’s a longer discussion about how the justification settings work, if you’re interested.
Sorry. My mistake.
I was looking at the first value and not the second. Thank you for clarifying.