Ruby's Nokogiri keeps complaining about HTML that looks perfectly fine to me. Below's an example of the affected HTML and the full error message.
<div class="media">
<figure id="post-image-figure-8" class="post-image-figure" style="max-width: 50%; ">
<img src="/file8-thumbl.jpg" class="post-image img-no-border" id="post-image-8" style="cursor: pointer; max-width: 100%;" onclick="openPostIMG(8)" data-url="/file8.jpg" data-width="960" data-height="540" data-id="8">
</figure>
</div>
/usr/lib/x86_64-linux-gnu/rubygems-integration/3.1.0/gems/nokogiri-1.13.10/lib/nokogiri/html4/document.rb:220:in ``read_memory': Parser without recover option encountered error or warning: 4:107: ERROR: Tag figure invalid (Nokogiri::XML::SyntaxError)
Tried to check with my browser's developer tools, but those didn't complain about any malformed HTML.
I fixed the issue by replacing node = Nokogiri::HTML.fragment(html) with node = Nokogiri::HTML5.fragment(html)