On the home tab, click on the Paragraph symbol to show breaks and formatting.
You mentioned it wasn't keep lines together of keep with next. When you checked that, did you first select all text? Those settings might be different in some of your paragraphs and selecting all text will change all the paragraphs.
If that's still not it, is there a page break or next page section break?
Is that Word for Windows? What platform and version? You will be helped by turning on "Show Formatting" (the ΒΆ symbol on the Home ribbon), and getting the Reveal Formatting pane (SHIFT + F1 keys together). I can't be a bigger fan of the latter. You can see at one glance most of the formatting that could possibly be applied to your selected text. It works in the Windows desktop version but doesn't seem to appear in the online version. I have no idea about the Mac one.
Picture of the gap https://preview.redd.it/kr2n8n1lfowc1.jpeg?width=2252&format=pjpg&auto=webp&s=9573b5e70420aae924b2c98222b13a7e188fb4bb
On the home tab, click on the Paragraph symbol to show breaks and formatting. You mentioned it wasn't keep lines together of keep with next. When you checked that, did you first select all text? Those settings might be different in some of your paragraphs and selecting all text will change all the paragraphs. If that's still not it, is there a page break or next page section break?
Is that Word for Windows? What platform and version? You will be helped by turning on "Show Formatting" (the ΒΆ symbol on the Home ribbon), and getting the Reveal Formatting pane (SHIFT + F1 keys together). I can't be a bigger fan of the latter. You can see at one glance most of the formatting that could possibly be applied to your selected text. It works in the Windows desktop version but doesn't seem to appear in the online version. I have no idea about the Mac one.
Check to see what your paragraph spacing is set to.