Fatal PHP Errors

We are getting various errors that seem to be slowing our site down and occasionally causing timeouts:

2019/07/02 12:09:57 [error] 128698#128698: *19263410 FastCGI sent in stderr: “PHP message: PHP Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 20480 bytes) in /www/sitename/public/wp-content/plugins/wp-cerber/common.php on line 1919PHP message: PHP Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 20480 bytes) in /www/sitename/public/wp-includes/class-wp-fatal-error-handler.php on line 65” while reading response header from upstream, client: 128.90.152.192, server: site.com, request: “GET /go/name HTTP/1.0”, upstream: “fastcgi://unix:/var/run/php7.3-fpm-site.sock:”, host: “site.com”

2019/07/02 12:09:19 [error] 128699#128699: *19263106 FastCGI sent in stderr: “PHP message: PHP Warning: mysqli_query() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1896PHP message: PHP Warning: mysqli_error() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1898PHP message: PHP Warning: mysqli_query() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1896PHP message: PHP Warning: mysqli_error() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1898PHP message: PHP Warning: mysqli_query() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1896PHP message: PHP Warning: mysqli_error() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1898PHP message: PHP Warning: mysqli_real_escape_string() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1864PHP message: PHP Warning: mysqli_real_escape_string() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1864PHP message: PHP Warning: mysqli_real_escape_string() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1864PHP message: PHP Warning: mysqli_real_escape_string() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1864PHP message: PHP Warning: mysqli_query() expects parameter 1 to be mysqli, null given in /www/site/public/wp-content/plugins/wp-cerber/common.php on line 1896PHP message: PHP Warning: mysqli_er