By default, the systems are usually distributed evenly on the page, but for this template they want to bunch up toward the top of the page.
I looked at every setting I know to check.
Take a look at Layout Options > Vertical Spacing > Vertical Justification. Your page is almost certainly under the first threshold; if you make that number smaller, then your page will appear justified. Changing the first setting to 0 means that all pages will be justified.
Do the bars on the second page belong still to page 1?
If yes, you might have dragged systems around in Engrave Mode. Reset the layout in menu Engrave > Format Music Frames.
If no, an alternative especially for percussion parts is to increase the inter-system gap, to be found also in Layout-Options > Vertical Spacing.