The automatic update setting you're interested in is found under Developer|Document Template>Template>Automatically update document styles. That said, the document attached to your post doesn't have that option checked.

The fundamental problems with your footnotes are three-fold:
1. Someone has overridden the line spacing on some in which the 'Footnote Text' Style is correctly applied with double spacing;
2. Your footnotes have empty paragraphs between them; and
3. Someone has replaced the 'Footnote Text' Style for some footnotes with the 'Normal' Style - which has single spacing applied.

Your document's last paragraph is even formatted in a user-defined Style named 'footnote tex'!


You really do need to learn how to use Styles properly, as they are at the heart of how Word works. See:
https://shaunakelly.com/word/styles/stylesms.html
http://www.addbalance.com/usersguide/styles.htm
https://www.word-tips.com/microsoft-word-styles/

To fix your footnotes, click on any of them, then press Ctrl-A, which will select all footnotes. Then apply the 'Footnote Text' Style to all footnotes and set the paragraph line spacing to Single. Next, go through all the footnotes and delete any paragraphs separating them (you'll need to select the second-last paragraph break in each footnote, not the last one).

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]