I already filed an issue about this in the theme repo (https://github.com/fedora-infra/fedora-mediawiki-theme/issues/1), but since that was the first issue EVER in that repo, I don't know how closely watched it is.

A recent commit added this to the screen-common.less file:

a:visited {
    color: inherit;
}

This (combined with the removal of underlines) is causing visited links to inherit the default text style — IOW, black text with no decoration. As a result, visited links are now indistinguishable from body text on the wiki.

At the bottom of https://fedoraproject.org/wiki/SELinux/Unsound_or_dangerous_SELinux_policy_practices, because I've visited "DSP packaging guide" already, it appears identical to any other body text. Only when I hover over the first, can I tell it's a link (because the underline appears).