Here's the code that causes the issue:

<table>
  <tr>
    <td>test</td>
    <td>test</td>
  </tr>
  <tr>
    <td>test</td>
    <td>
      <span>test</span>

      <table>
        <tr>
          <td>test</td>
          <td>test</td>
          <td>test</td>
        </tr>
      </table>
    </td>
  </tr>
</table>

The result:

If I wrap the nested <span> and <table> in a single <div>, it works as expected:

Initially I thought this must've been an issue with Jekyll's markdown parsers. See these issues for more information and more cases of odd/wrong behavior:

gettalong/kramdown#803
kramdown/parser-gfm#39

But then I tested those gems directly, and they didn't produce the problems. Eventually I narrowed down the problem to just jekyll-spaceship. If I have it on, this breaks.

Here's a minimal reproducible example. If you comment out the spaceship plugin in the gemfile, it works.

minimal-reproduction.zip