AppStream description appears as "(null)"

I recently added a paragraph to our app’s description in its .metainfo.xml file. The app’s About page has since been updated, but the new paragraph appears simply as “(null)”.

Is this perhaps because the paragraph contains an unordered list tag, list items or <em> tags? The XML file passes the org.freedesktop.appstream-glib validate test, and the description respects documented AppStream limitations, but maybe there are additional limitations imposed by Flathub? What else might cause a paragraph to be replaced by “(null)”?

I have opened an issue (#4157) for this.

The unordered list cannot appear inside a paragraph. When the <p> tag is removed, the list is displayed correctly, although the <em> tag appears verbatim in the text.