Error when logging in as a subscriber

We are experiencing problems with our website in that everytime we try to login a subscriber with correct credentials, they get redirected back to the login page.

I already tinkered with w3tc settings following the instructions from this link: https://www.ads-software.com/support/topic/logged-users-on-cached-pages-are-not-logged/

Basically, these fixes were centered around the page cache and browser cache settings on the plugin. However, it still has not been successful in repairing this specific problem. I already contacted w3tc with regards to this issue, and I followed the same things they recommended which leads me to look into other outlets that might be causing it.

I tried adding a nonce to the redirect url by:

$redirect_url = wp_nonce_url(site_url(‘/feature-selection/’, ‘https’), ‘redirect’, ‘redirect_nonce’);
$redirect = (!empty($FORMPOST[‘redirect’]) ? $FORMPOST[‘redirect’] : $redirect_url);

But still no luck. Please help.

The page I need help with: [log in to see the link]