Unable to upload a file from UI component using dynamic rows in magento2.3.1

My UI component form fieldset

<field name="file">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="dataType" xsi:type="string">string</item>
                    <item name="source" xsi:type="string">template</item>
                    <item name="label" xsi:type="string" translate="true">File</item>
                    <item name="dataScope" xsi:type="string">file</item>
                    <item name="visible" xsi:type="boolean">true</item>
                    <item name="formElement" xsi:type="string">fileUploader</item>
                    <item name="elementTmpl" xsi:type="string">ui/form/element/uploader/uploader</item>
                    <item name="previewTmpl" xsi:type="string">Kensium_Onlineguide/image-preview</item>
                    <item name="required" xsi:type="boolean">false</item>
                    <item name="uploaderConfig" xsi:type="array">
                        <item name="url" xsi:type="url" path="cms/onlineguide/savefile"/>
                    </item>
                </item>
            </argument>
   </field>

And admin controller execute method

public function execute()
    {
        try {
            $result = $this->imageUploader->saveFileToTmpDir('file');

            $result['cookie'] = [
                'name' => $this->_getSession()->getName(),
                'value' => $this->_getSession()->getSessionId(),
                'lifetime' => $this->_getSession()->getCookieLifetime(),
                'path' => $this->_getSession()->getCookiePath(),
                'domain' => $this->_getSession()->getCookieDomain(),
            ];
        } catch (\Exception $e) {
            $result = ['error' => $e->getMessage(), 'errorcode' => $e->getCode()];
        }
        return $this->resultFactory->create(ResultFactory::TYPE_JSON)->setData($result);
    }

And Created custom Model ImageUploader.php below

public function saveFileToTmpDir($fileId)
    {
        $baseTmpPath = $this->getBaseTmpPath();

        $uploader = $this->uploaderFactory->create(['fileId' => $fileId]);
        $uploader->setAllowedExtensions($this->getAllowedExtensions());
        $uploader->setAllowRenameFiles(true);

        $result = $uploader->save($this->mediaDirectory->getAbsolutePath($baseTmpPath));

        if (!$result) {
            throw new \Magento\Framework\Exception\LocalizedException(
                __('File can not be saved to the destination folder.')
            );
        }

        $result['tmp_name'] = str_replace('\\', '/', $result['tmp_name']);
        $result['path'] = str_replace('\\', '/', $result['path']);
        $result['url'] = $this->storeManager
                ->getStore()
                ->getBaseUrl(
                    \Magento\Framework\UrlInterface::URL_TYPE_MEDIA
                ) . $this->getFilePath($baseTmpPath, $result['file']);
        $result['name'] = $result['file'];

        if (isset($result['file'])) {
            try {
                $relativePath = rtrim($baseTmpPath, '/') . '/' . ltrim($result['file'], '/');
                $this->coreFileStorageDatabase->saveFile($relativePath);
            } catch (\Exception $e) {
                $this->logger->critical($e);
                throw new \Magento\Framework\Exception\LocalizedException(
                    __('Something went wrong while saving the file(s).')
                );
            }
        }

        return $result;
    }

This customization gives the error:

The file was not uploaded with error code :666

Could anyone help to fix this issue?