The developers one more time checked the issue and saw that the issue is caused by Defender Pro plugin. Please see the recorded video below:

https://www.screencast.com/t/ACB909s2

The error message:

<br><b>Uncaught Error</b>: Call to a member function to_array() on null in <b>/var/web/site/public_html/wp-content/plugins/wp-defender/app/module/audit/component/comment-audit.php</b> on line <b>155</b><br><ul><li>processGenericComment()</li><li>invokeArgs()<br><span class="qm-info qm-supplemental">wp-content/plugins/wp-defender/app/module/audit/event-abstract.php:253</span></li><li>build_log_data()<br><span class="qm-info qm-supplemental">wp-content/plugins/wp-defender/app/module/audit/component/audit-api.php:360</span></li><li>WP_Defender\M\A\C\{closure}()<br><span class="qm-info qm-supplemental">wp-includes/class-wp-hook.php:290</span></li><li>apply_filters()<br><span class="qm-info qm-supplemental">wp-includes/class-wp-hook.php:312</span></li><li>do_action()<br><span class="qm-info qm-supplemental">wp-includes/plugin.php:478</span></li><li>do_action()<br><span class="qm-info qm-supplemental">wp-includes/comment.php:1429</span></li><li>wp_delete_comment()<br><span class="qm-info qm-supplemental">wp-content/plugins/wpdiscuz-frontend-moderation/class.wpDiscuzFrontEndModeration.php:403</span></li><li>deleteComment()<br><span class="qm-info qm-supplemental">wp-includes/class-wp-hook.php:288</span></li><li>apply_filters()<br><span class="qm-info qm-supplemental">wp-includes/class-wp-hook.php:312</span></li><li>do_action()<br><span class="qm-info qm-supplemental">wp-includes/plugin.php:478</span></li><li>do_action()<br><span class="qm-info qm-supplemental">wp-admin/admin-ajax.php:175</span></li></ul><p>Es gab einen kritischen Fehler auf deiner Website.</p><p><a href="https://wordpress.org/support/article/debugging-in-wordpress/">Erfahre mehr über die Fehlerbehebung in WordPress.</a></p>

Even if you deactivate the wpDiscuz plugin, each time when you try to delete the comments from the backend the issue still exists.

I talked with the developer and they did thorough testing of any compatibility issues. They say the problem is caused by the frontend moderation plugin. 

So I would ask you to have another closer look at the problem, maybe you can find the issue.

Best wishes

Johannes

To find the reason of the issue the developers will need to modify the wpDiscuz Frontend Moderation add-on files. Please read this article to learn more about plugin editing feature: https://www.webhuntinfotech.com/enable-theme-plugin-editor-wordpress/

The issue is caused by the Defender Pro plugin.

It will be better if you contact the Defender Pro plugin support and ask them that question.

What do you mean by that?

Could you please open a plugin editing feature to allow us to check it.

I am afraid the issue is still there for me.

Best

Johannes

This will be fixed in the next version update.

In case if you want to fix it as soon as possible please follows the steps below to get it resolved:

1. Open the /wp-content/plugins/wpdiscuz/class.WpdiscuzCore.php file

2. Find the following line (1068 line):

wp_register_script('wpdiscuz-jquery-cookie', plugins_url(WPDISCUZ_DIR_NAME . '/assets/third-party/wpdcookiejs/customcookie.js'), array('jquery'), $this->version, true);

3. Replace with the following one:

wp_register_script('wpdiscuz-jquery-cookie', plugins_url(WPDISCUZ_DIR_NAME . '/assets/third-party/wpdccjs/wpdcc.js'), array('jquery'), $this->version, true);

Don't forget to delete all caches and press CTRL+F5(twice) on the frontend before checking.

Please send it as a PM message.