first check all rpm are up to date contribs and core.
any httpd.conf custom template could be related to this issue.
The thing is httpd 2.4 is between two way of handling access the former one (allow|deny) and the new way with Require/satisfy.
if you have any old way allowing access the previous way to root then this will override the other new that are used for phpmyadmin, and might create such a behaviour. so do not just « don’t think ». check