Noticed in mediawiki-errors in both wmf.8 and wmf.9
[XBuwowpAAEIAACIQ3x8AAAAL] /w/load.php?debug=false&lang=frr&modules=startup&only=scripts&skin=vector Exception from line 1535 of /srv/mediawiki/php-1.33.0-wmf.8/includes/resourceloader/ResourceLoader.php: JSON serialization of config data failed. This usually means the config data is not valid UTF-8.
[XBuxzQpAICwAAJHqxlwAAAAS] /w/load.php?debug=false&lang=frr&modules=startup&only=scripts&skin=vector Exception from line 1535 of /srv/mediawiki/php-1.33.0-wmf.9/includes/resourceloader/ResourceLoader.php: JSON serialization of config data failed. This usually means the config data is not valid UTF-8.
There are two similar closed tasks: