Proxy request for Kickstart file fails

For some reason my proxy gets a 500 from my foreman server when making a
request for /unattended/provision?token=$TOKEN for a host's KS file.

On the Foreman server, I see this in the log

2017-01-23 13:54:52 5f983baa [app] [F]
> ActionController::RedirectBackError (No HTTP_REFERER was set in the
request to this action, so redirect_to :back could not be called
successfully. If this is a test, make sure to specify request.env[
> app/controllers/application_controller.rb:293:in process_error' > app/controllers/application_controller.rb:117:insmart_proxy_exception'
> lib/middleware/catch_json_parse_errors.rb:9:in call' > lib/middleware/tagged_logging.rb:18:incall'

I had this issue last week and for some reason recreating the hosts
resolved the issue, but I've done that a couple times here to no avail.

Any suggestions on how to debug? I don't have this problem with other smart