It's fairly well known at this point that Wowhead uses an ad framework with autorefreshing ads. If you leave your browser open on the page without proper adblock extensions installed, you'll get an enormous amount of traffic usage. In the last month there have been claims that this has increased, with statements coming from Wowhead that they have actually been reducing the number of ads and the autorefresh timer.
Looking deeper into the page code, I believe I have found the culprit: the Stanza calendar that was added recently.
Looking at the Wowhead page in Chrome with no adblockers installed, it can be seen that the main page pulls down the monkeybroker ad framework:
Looking further down in the sources tab, there's also a zam-wow element, which expanding it, reveals another request for the monkeybroker ad scripts:
Debugging finds that this zam-wow section is tied to the stanza calendar:
<div class="stanzacal" stanzacal="zam-wow" site="zam-wowhead" width="100%" height="250px" data-injected="true" style="width: 100%; height: 250px;"><iframe sandbox="allow-forms allow-popups allow-scripts allow-pointer-lock allow-same-origin" src="https://stanza.co/timeline/zam-wow?embed=true&site=zam-wowhead" style="width: 1px; min-width: 100%; height: 100%; border: none; outline: 0px;"></iframe></div>
TL;DR: Wowhead is giving you two autorefreshing ad instances when you visit their page without an adblocker. This happened when the Stanza calendar was introduced a few weeks ago, which is why people have seen more lag and resource usage on Wowhead in the last month. Even though there are no ad sections visible on the Stanza row displayed on wowhead, they are present on the original site, meaning they still have to be requested and rendered, in addition to the cookies and tracking scripts that get pulled. Effectively, the amount of stuff tied to ads has nearly doubled with the introduction of this feature to the site.