PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'remove_wpcf7' not found or invalid function name

Apologies for this broad question but I am not hugely familiar with the Error Log entries at present. Any directives on where to begin the relevant research, would be greatly appreciated.

For the past 12 months, I have had the Google Authenticate Plugin, installed on a WordPress powered eCommerce website I work on. There had been no issues with the Plugin until a recent VPS and WordPress update. Since said updates, the Google Authenticate Plugin does not recognise any of the inputted codes. I am not sure if the error is being triggered by the WordPress update or the VPS itself.

I then checked the error_log and saw the below entry when trying to use the Google Authenticate Plugin:

mod_fcgid: stderr: PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'remove_wpcf7' not found or invalid function name in /var/www/vhosts/example.com/httpdocs/wp-includes/class-wp-hook.php on line 286, referer: https://www.example.com/wp-admin/plugins.php

Troubleshooting

As standard, I deactivated all Plugins (Except for the WooCommerce Plugin) as well as the WordPress Theme I had created. I then simply activated WordPress' Twenty Seventeen Theme. The error still persisted; leaving me wondering just what is causing the issue.

I can see there is a reference to WordPress' core files. Maybe there is some incompatibilities?

Any directives on this, would be greatly appreciated ... Even if to just help me expand on this question.

Finally found the solution ... It related to the Server Time Settings.

If anyone else is experiencing a similar issue with their Google Authentication feature, you will need to ensure your Server's time settings are in sync with the 'Internet's Clock'.

1. Login into your VPS;
2. Head to Tools & Settings > General Settings > System Time;

3. Here, you should have a screen that looks something like:

   

4. Ensure that the Date & Time > Update system time is deselected;

5. Ensure that Network time > Synchronize system time is selected;
6. Then within Network time > Domain name or IP, enter 3.pool.ntp.org and select 'Ok'. It was this step, which I needed to do in order to fix my own issue.