Man page links do not work when there is no character afer the section number in the man file.
For example, a man code like this :

.Xr ssh 1

produces a Xml like this :

<Xr>ssh 1</Xr>

so, the XSL transformation "fails" and produce an invalid link as following :

ssh()

This bug appears when there are no space + another character after the section number in the man file.

I managed to fix it by changing the man2html.xsl.

File : man2html.xsl
Line : 322

<!-- Cross reference -->
<xsl:template match="Xr">
  <xsl:variable name="manpage" select="substring-before(string(.), ' ')"/>
  <xsl:variable name="sectiontmp" select="substring-before(substring-after(string(.), ' '), ' ')"/>
  <xsl:variable name="extra" select="substring-after(substring-after(string(.), ' '), ' ')"/>
  <xsl:choose>
        <xsl:when test="$sectiontmp=''">
                  <xsl:variable name="section" select="substring-after(string(.), ' ')"/>
                  <a>
                    <xsl:attribute name="href">
                      <xsl:text>man:</xsl:text>
                      <xsl:value-of select="$manpage"/>
                      <xsl:text>(</xsl:text>
                      <xsl:value-of select="$section"/>
                      <xsl:text>)</xsl:text>
                    </xsl:attribute>
                    <xsl:value-of select="$manpage"/>
                    <xsl:text>(</xsl:text>
                    <xsl:value-of select="$section"/>
                    <xsl:text>)</xsl:text>
                  </a>
        </xsl:when>
        <xsl:when test="$sectiontmp!=''">
                  <xsl:variable name="section" select="$sectiontmp"/>
                  <a>
                    <xsl:attribute name="href">
                      <xsl:text>man:</xsl:text>
                      <xsl:value-of select="$manpage"/>
                      <xsl:text>(</xsl:text>
                      <xsl:value-of select="$section"/>
                      <xsl:text>)</xsl:text>
                    </xsl:attribute>
                    <xsl:value-of select="$manpage"/>
                    <xsl:text>(</xsl:text>
                    <xsl:value-of select="$section"/>
                    <xsl:text>)</xsl:text>
                  </a>
        </xsl:when>
  </xsl:choose>
  <xsl:value-of select="$extra"/>
</xsl:template>

I did not find another way that duplicate the code.