In case anyone stumbles across this, I've encountered similar problems with my excessively gregarious footnotes, and here are my current workarounds for my Kindle Oasis:
For basic multi-paragraph footnotes, if you use indentation instead of block divisions to indicate paragraphs, you can wrap the entire footnote in one <p> tag and use <br> wherever you want a paragraph break. This is neither undocumented nor incorrect html and looks fine in the popup and the footnote page.
However,
any block level separation will trigger the single paragraph issue. I've tried every torturous-yet-valid combination of css and html I know of; it appears the rendering engine is simply aware of the divide and will cut off multiple paragraphs.
I decided in this case it's better to jump directly to the note, and you can force this behavior by omitting the epub:type="noteref" in the link to the footnote, so your initial link is just
<p>The text<a id="1" href="#foot1">1</a></p>