Not seeing any HTTPCode_Backend Response on the Classic Load Balancer logs

Hello,
I have a classic LB with TCP 443 port forwarding to my backend instances, where I have SSL certificate configured on IIS.
IIS logging is enabled.
When deliberately hitting some URLs with wrong parameters, I get 403 errors from IIS, but I do not see any HTTPCode_Backend in teh CLoudwatch
I don't see it in the Athena when trying to analyze the ELB logs either.
elb_repsonse_code and backend_response_code in Athena are both empty.

Can anyone point me in the troubleshooting direction?>

Thanks