The message 'jsonschema-invalid-notinenum' is being passed wrong parameters, at least sometimes (T123840).

$msg = JsonUtil::uiMessage( 'jsonschema-invalid-notinenum', $this->node, $this->getDataPathTitles() );

Where JsonUtil::uiMessage is a wrapper for wfMessage and $this->node is an array (possibly associative) representing current node. wfMessage interprets this array as message parameters, ignoring the second function call parameter. Not sure how this ever worked.