Up spacers do not add space between top visible stave and top page edge when "Format > Style > Score > Hide empty staves within systems" is selected and there are (hidden) empty staves above the top visible stave?
Apologies for the title gore.
I'm not sure if this is an intended feature or a bug, however in Musescore 2 you could use the up spacer to add space between the top visible stave and the top page edge, even if there were hidden additional staves above the top visible stave. That doesn't appear to work in MS3.
I have this issue both on scores imported from v2 into v3, as well as can recreate the issue by creating a score in MS3 (attached: try moving the top spacer).