Sometimes modSecurity may determine your website as vulnerable and can block your access to the server showing error 403. Even for clean installation, this may happen, because somethimes modSecurity CRS determine your script or plugin as malicious and is blocking some java, json or ajax requests.
In order to avoid this false-positive issues, please add this lines in your .htaccess file from your root directory.
<IfModule mod_security.c>
SecRuleRemoveById 941100 942100
</IfModule>
Save file and clear cache of your website, by flashing the cache, or pressing CTRL & F5 buttons together on the keyboard.
