Problem
From T221347#5122170 and T221347#5122194:
On 2019-04-18 from 10:00 UTC (possibly earlier), the code in mediawiki/Skin.php on the mw1274 server appeared to have changed in opcache. This lasted until 13:00 when the opcache was manually cleared.
function getLogo() { - return $this->getConfig()->get( 'Logo' ); + return $this->getConfig()->get( 'Kogo' ); }