The Next Page section break will always start a new page.

That there is a blank page after it before other text means something else is going on.

Try using Shift+F1 and other Reveal Formatting techniques to figure it out. Look for more page or section breaks and for formatting in the text following the blank page that would cause a page break.

Paragraph formatting that may be involved:
Page break before
Keep with next (most heading styles)
Keep lines together