when you use the “alpha channel:00” workaround to hide items, in this case bar rests, they still are shown in exported pdf’s from “print”.
the workaround of the workaround is to export grafics in color.
I really hope there will be “in due time” 
a more direct way to hide items.
I’m curious why you can’t “hide” the bar rests using Edit > Remove Rests, which is the feature designed to meet this requirement?
why I cant hide rests:
OK, fair enough! But for what it’s worth, it’s quite possible that the way a more generalised “hide” feature might work, should we ever make one (and I am by no means completely in favour of doing so), would cause the same spacing issue, because if Dorico doesn’t draw something, it doesn’t space it either.