This was reported by the link checker as a broken fragment (it is but there is a more serious issue afoot):

<p class="MsoNormal"><span style="color:black">MQTT V3.1 Protocol Specification.</span></p>

<p class="MsoNormal"><a href="#_Hlk354734548"><span style="color:windowtext">http://public.dhe.ibm.com/software/dw/webservices/ws-mqtt/mqtt-v3r1.htmlhttp://www.ibm.com/developerworks/webservices/library/ws-mqtt/index.html.</span></a><i>
</i></p>

The <a href="#_Hlk354734548"> was reported as a broken fragment, which is true but the real issue is that the link for the spec doesn't match the href in the <a> element.