Same problem for me – further info
Thank you for your work on Wordfence, including Falcon.
The site was on WordPress 3.8.x with WordPress 5.0.2; Falcon was working fine.
Upgraded WordPress to 3.9, and Wordfence from 5.0.2 to 5.0.3; the site worked fine (the upgrade disabled Falcon).
When I enabled Falcon, I got “Internal Server Error”; restoring .htaccess brought the site back OK.
The error log shows: /var/www/html/wordpress/.htaccess: order not allowed here
Re-enabling Falcon and commenting out line 2 of .htaccess: “Order Deny,Allow”, the site seems OK,
although it may not be secure or working totally correctly without that line.
Now running on Basic Caching until this is fully resolved.
