First thing. In your Text Inspector : More tab, deselect Prevent widow & orphan lines. Secondly, review your Wrap Inspector settings for Object Causes Wrap : Above and Below. You may have to change the wrap style with the table nearing the document bottom. If these two Inspector activities have solved the mysterious space issue, then disregard the next paragraph.
Place your insertion point at the beginning of your document. Open the Text Inspector to its Text tab. Repeatedly tap the down-arrow key while watching the Line, and before/after paragraph settings. If you encounter an unexpected setting in these fields, that may also explain the gap in your document.
Lastly, look at your Layout Inspector, and ensure that the Layout margins at the bottom are all 0, and in the Document Inspector, that there are no surprises in there regarding margin settings.