httpsdocs home directory is used instead of httpdocs for Plesk site: 404 not found

Symptoms

1. Website or specific page is not accessible:

   404 not found

2. /var/www/vhosts/example.com/httpsdocs home directory is used by site instead of /var/www/vhosts/example.com/httpdocs/
3. Error in /var/www/vhosts/system/example.com/logs/error_log:

   AH01276: Cannot serve directory /var/www/vhosts/example.com/httpsdocs/: No matching DirectoryIndex (index.php) found, and server-generated directory index forbidden by Options directive

Cause

Compatibility mode is enabled for the legacy option in  Domains > example.com > Hosting Settings. Check Site shows 403 Forbidden error via HTTPS for more information. Once the mode is disabled, the operation cannot be reverted.

Resolution

1. Log in to Plesk
2. Go to Domains > example.com > Hosting Settings
3. Deactivate Compatibility mode for the legacy option “Separate SSL/TLS and non-SSL/TLS content”