Your landscape page contains a table which is not in-line-with text or otherwise anchored to the text. It is free-floating. All that is in the body of the page is the table. The caption for the table is inside the table (not necessarily a good idea).
I had no trouble moving it to the center of the page by grabbing the handler but it is not changed by the alignment setting.
I then tried recreating your document. When I pasted in the textbox for your landscape footer, it moved the table to the top when it was in the center using the Vertical alignment. The same thing did not happen with the textbox for the header.
I copied the one for the header and put it in the left position for a footer and typed in the page number.
I cannot explain it. Life is too short.
Here is a sample of what I did:
Dropbox - SampleAlignmentProblemdelete.docx - Simplify your life