There are a few issues that can be caused by load balancers.
Second, the headers may get messed up by the load balancer. Internally, Looker uses the following settings on our proxy server to avoid this issue:
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header Accept-Encoding "";
proxy_set_header Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
# Uncomment if behind ELB
proxy_set_header X-Forwarded-Proto https;