I believe the problem is that your web host is seeing the BPS Pro MScan malware checking code/filters as malicious and is deleting or nulling this MScan file that contains the BPS Pro MScan malware checking code: /bulletproof-security/includes/mscan-ajax-functions.php
Code line 83 in the /bulletproof-security/bulletproof-security.php file
// MScan AJAX functions
require_once( WP_PLUGIN_DIR . '/bulletproof-security/includes/mscan-ajax-functions.php' );
As a workaround for now do these steps:
1. Use FTP or your web host control panel file manager, open and edit the /bulletproof-security/bulletproof-security.php file.
2. Comment out Code line 83 in the /bulletproof-security/bulletproof-security.php file with 2 forward slashes as shown below.
// MScan AJAX functions
//require_once( WP_PLUGIN_DIR . '/bulletproof-security/includes/mscan-ajax-functions.php' );
We are currently in the process of figuring out the best way to deal with this issue/problem permanently and will have a permanent solution in the next BPS Pro version release.
Reference forum topic: https://forum.ait-pro.com/forums/topic/mscan-troubleshooting-questions-problems-and-code-posting/#post-34091