funny bug with extract and string concat (WAMP)

<?php

/**
 * funny bug with extract and string concat
 * that results in ERR_CONNECTION_RESET (WAMP)
 */

//custom styles I get from the CMS editor
$json = '{
    "classname": ".b-1067",
    "styles": {
        "only screen": {
            "background": "#E6F0FA",
            "padding-top": "4rem 0 2rem",
            "margin-top": "0"
        },
        "only screen and (min-width: 720px)": []
    },
    "childStyles": {
        "only screen": [
            ".wrap { max-width: 1200px; }"
        ],
        "only screen and (min-width: 720px)": [
            ".grid__item { width: 50%; }",
            ".grid__item { border-width: 0 0.5rem 0.5rem; }"
        ]
    }
}';

//renaming $styles to $data prevents the bug
$styles = json_decode($json, true);
extract($styles); //destruct this variable to give me $classname, $styles, $childStyles


//this outer loop would be the different CMS content blocks
//removing this loop prevents ERR_CONNECTION_RESET and reveals the error message (undefined index)
$blocks = array(1,2,3,4,5,6,7,8,9);
foreach($blocks as $block) {

    foreach($styles as $mq => $attributes) {

        //echo main styles ...

        //echo nested child styles
        foreach($childStyles[$mq] as $style) {
            echo $classname .' '. $style; //ERR_CONNECTION_RESET (WAMP)

            //works:
            //echo $classname;
            //echo ' ';
            //echo $style;

            echo '<hr />';
        }
    }
}