I have recently visited the page Incubator:Community Portal (link). Till yesterday, there was no issue with the display. But today, when I viewed that page, the width of the page starting from the section contents has decreased. You can compare the discussion pages like the Village Pump(Technical) of English wikipedia for reference. I have checked with Mozilla Firefox as well as Google Chrome (version 74.0.3729.169). I didn't see this issue in other pages.
See the HTML source of that page, via your browser's developer tools: https://developer.chrome.com/devtools
<div class="communityportal-news" style="margin-right:25em; margin-bottom:2em;">
That's what's exactly provided by the Community Portal Template on incubator.wikimedia.org.
On-wiki content is not handled in Phabricator, hence closing this task as invalid.