Magento – Magento 2 Notice: Undefined index RendererFactory.php on line 64

I had the same problem.

After searching the source of Magento 2.2.4 I found the function in file (vendor\magento\module-catalog-inventory\Model\Configuration.php):

public function getDefaultScopeId()
{
    // TODO: should be fixed in MAGETWO-46043
    // "0" is id of admin website, which is used in backed during save entity
    return 0;
}

In my case I modify Store parameters at "Stores > All Stores" and my actual store_id/scope_id was 1 and not 0. After changing "return 0" to "return 1", my problem was solved.

As this is anyhow TODO for Magento I expect, that in next upgrade this will be solved and all my modification will be overwritten and everything should work at that time...

Add the following code in the app/etc/di.xml file

<type name="Magento\Cms\Model\Wysiwyg\CompositeConfigProvider">
    <arguments>
        <argument name="variablePluginConfigProvider" xsi:type="array">
            <item name="default" xsi:type="string">Magento\Variable\Model\Variable\ConfigProvider</item>
        </argument>
        <argument name="widgetPluginConfigProvider" xsi:type="array">
            <item name="default" xsi:type="string">Magento\Widget\Model\Widget\Config</item>
        </argument>
        <argument name="wysiwygConfigPostProcessor" xsi:type="array">
            <item name="default" xsi:type="string">Magento\Cms\Model\Wysiwyg\DefaultConfigProvider</item>
        </argument>
        <argument name="galleryConfigProvider" xsi:type="array">
            <item name="default" xsi:type="string">Magento\Cms\Model\Wysiwyg\Gallery\DefaultConfigProvider</item>
        </argument>
    </arguments>
</type>

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