Word suppresses Space Before after natural page breaks, so I have to assume
you're inserting either a manual page break or a section break or you have
formatted the paragraph as "Page break before."

If you have made "Page break before" part of the style, then you can omit
the Space Before from the style. If it's applied as direct formatting, then
you'll also have to remove the Space Before as direct formatting.

If you've inserted a manual page break, you may be able to work around it by
using a combination of "Keep with next" and "Keep lines together" in the
paragraphs you want to go to the next page. It's generally best to avoid
manual page breaks insofar as possible.

There is a compatibility option (in some versions of Word) to "Suppress
Space Before after a hard page or column break." This should be used only as
a last resort. Also, it doesn't affect section breaks. But if you have a
large enough break to need a section break, then you also have a heading
that either deserves a lot of Space Before (as at the beginning of a book
chapter) or you have a heading that always occurs at the beginning of a
section and consequently could be defined to have no Space Before.