List with more than one level generates error: "Text elements must have sufficient color contrast."

How to reproduce:
List with two levels or more. No CSS needed.

<ul>
  <li>Lorem
    <ul>
      <li>Ipsum</li>
    </ul>
  </li>
</ul>

Plugin says: "Element's background color could not be determined because it is overlapped by another element."
Tested with Axe-core and browser plugin. Chrome on MacOS.