I have seen this somewhere but can’t seem to find it now… the whole concert band score is crammed together; is there a global tool that spreads the staff apart?
The other possibility is that you’ve inserted a manual page break and the option to “wait for next” is set. Either deleting the frame break or unticking that property will allow things to reflow properly. (This is presuming the settings Lillie linked to are already correct, of course.)