tidy reports the following:

build/linux-x86_64-server-release/images/docs/./api/java.base/java/lang/module/package-summary.html:99:6: Warning: missing </a> before <a>
build/linux-x86_64-server-release/images/docs/./api/java.base/java/lang/module/package-summary.html:99:95: Warning: discarding unexpected </a>

The HTML shows nested <a> tags:
 <h1><a id="resolution"><a id="ModuleResolution" class="searchTagResult">Module Resolution</a></a></h1>

This is causes by the following
src/java.base/share/classes/java/lang/module/package-info.java:37

 * <h1><a id="resolution">{@index "Module Resolution"}</a></h1>

Since {@index} expands to an <a> tag, it wo0uld be better to rewrite this as
<h1><a id="resolution"></a>{@index "Module Resolution"}</h1>

Separately, nearby, tidy also reports:

build/linux-x86_64-server-release/images/docs/./api/java.base/java/lang/String.html:3593:2: Warning: trimming empty <p>

caused by the excess <p> on String.java:2894

     * If {@code n == 0} then the line remains unchanged. However, line
     * terminators are still normalized.
     * <p>