Unable to edit single or structures, channels working fine after update to Craft 3 Working in devMode, when trying to edit an existing single or structure entry, I get an InvalidArgument error

yii\base\InvalidArgumentException: Syntax error. in ...vendor/yiisoft/yii2/helpers/BaseJson.php:133

if (isset($availableErrors[$lastError])) {
    throw new InvalidArgumentException($availableErrors[$lastError], $lastError);
}


I notice in Chrome tools I get a bunch of Craft is not defined errors any ideas?
Was an issue with my Simple.json redactor config

Was

{
    buttons: [bold, italic],
    toolbarFixed: true
}


Needed to be

{
    "buttons": ["bold", "italic"],
    "toolbarFixed": true
}