Yeah, after you enter a password, elog redirects to what it finds in "URL". You can trace that by opening "development tools" in Google Chrome, go to "network" and watch packets going back and forth. I never worked with the load balancer, but maybe you need a different "URL" containing a '/' at the end?
I also tried the default configuration (example config) and it that works behind the load balancer. So I guess it's related to the password-page, which causes this redirect loop? Our logbooks are all password protected, so when a logbook URL is clicked, it should first present the login-form, and that's where it chokes.