Magento 2 – Backend Grid Inline Edit Not Working

I've a backend grid that uses the UI component and itself works and shows up fine, but I can't get inline edit working. I've tried following a couple of tutorials and examples and I can't figure out what I'm missing here. Nothing happens when I click the supposedly editable column.

Here are some relevant snippets from my code:

UI component xml-file:

<columns name="spinner_columns">
    <selectionsColumn name="ids">
        <argument name="data" xsi:type="array">
            <item name="config" xsi:type="array">
                <item name="editorConfig" xsi:type="array">
                    <item name="selectProvider" xsi:type="string">vendor_module_threshold_listing.vendor_module_threshold_listing.spinner_columns.ids</item>
                    <item name="enabled" xsi:type="boolean">true</item>
                    <item name="indexField" xsi:type="string">threshold_id</item>
                    <item name="clientConfig" xsi:type="array">
                        <item name="saveUrl" xsi:type="url" path="vendor_module/threshold/inlineEdit"/>
                        <item name="validateBeforeSave" xsi:type="boolean">false</item>
                    </item>
                </item>
                <item name="childDefaults" xsi:type="array">
                    <item name="fieldAction" xsi:type="array">
                        <item name="provider" xsi:type="string">vendor_module_threshold_listing.vendor_module_threshold_listing.spinner_columns_editor</item>
                        <item name="target" xsi:type="string">startEdit</item>
                        <item name="params" xsi:type="array">
                            <item name="0" xsi:type="string">${ $.$data.rowIndex }</item>
                            <item name="1" xsi:type="boolean">true</item>
                        </item>
                    </item>
                </item>
            </item>
        </argument>
    </selectionsColumn>
...
<column name="threshold">
        <argument name="data" xsi:type="array">
            <item name="config" xsi:type="array">
                <item name="editor" xsi:type="array">
                    <item name="editorType" xsi:type="string">text</item>
                    <item name="validation" xsi:type="array">
                        <item name="required-entry" xsi:type="boolean">true</item>
                    </item>
                </item>
                <item name="filter" xsi:type="string">text</item>
                <item name="label" xsi:type="string" translate="true">Threshold</item>
            </item>
        </argument>
    </column>

Vendor/Module/Controller/Adminhtml/Threshold/InlineEdit.php

<?php

namespace Vendor\Module\Controller\Adminhtml\Threshold;

class InlineEdit extends \Magento\Backend\App\Action
{
    protected $jsonFactory;

    public function __construct(
        \Magento\Backend\App\Action\Context $context,
        \Magento\Framework\Controller\Result\JsonFactory $jsonFactory
    ) {
        parent::__construct($context);
        $this->jsonFactory = $jsonFactory;
    }

    public function execute()
    {
        /** @var \Magento\Framework\Controller\Result\Json $resultJson */
        $resultJson = $this->jsonFactory->create();
        $error = false;
        $messages = [];

        $writer = new \Zend\Log\Writer\Stream(BP . '/var/log/test.log');
        $logger = new \Zend\Log\Logger();
        $logger->addWriter($writer);
        $logger->info('inlineEdit triggered!');

        if ($this->getRequest()->getParam('isAjax')) {
            $postItems = $this->getRequest()->getParam('items', []);
            if (!count($postItems)) {
                $messages[] = __('Please correct the data sent.');
                $error = true;
            } else {
                foreach (array_keys($postItems) as $entityId) {
                    /** load your model to update the data */
                    $model = $this->_objectManager->create('Vendor\Module\Model')->load($entityId);
                    try {
                        $model->setData(array_merge($model->getData(), $postItems[$entityId]));
                        $model->save();
                    } catch (\Exception $e) {
                        $messages[] = "[Error:]  {$e->getMessage()}";
                        $error = true;
                    }
                }
            }
        }

        return $resultJson->setData([
            'messages' => $messages,
            'error' => $error
        ]);
    }
}

InlineEdit.php is never triggered by the way.
Any ideas what's wrong/how to fix this? Help would be much appreciated.