Experiencing HTTP ERROR 500 – PHP Fatal error

The file mentioned in the error message belongs to the plugin All In One SEO. I would recommend you to contact their support: https://www.ads-software.com/support/plugin/all-in-one-wp-security-and-firewall/

There is already a similar topic there: https://www.ads-software.com/support/topic/500-error-after-update-9/

@threadi I think you meant to say All in One WP Security, not All in One SEO. But I understand the confusion ??

I faced the similar issue during past. Check if admin username and password are same in your hosting and try to update php version.

Problem eventually resolved by the hosting provider. Thanks