I have Windows Server 2012 R2 Standard with IIS 8.5.
I added the enhanced logging custom filed for our website (on site level): X-FORWARDED-FOR as described in: https://www.iis.net/learn/get-started/whats-new-in-iis-85/enhanced-logging-for-iis85 When I click Apply the site stops logging completely. No errors are visible in the Application Event log. After I remove the custom field the login resumes. I need this to capture to original client IP from Cloudflare.