http://box:3000 does not display ZIM's since kiwix-tools 0.6.0 (PR #845) were merged on 2018-06-20. All nightly builds of kiwix-tools fail in the same way since Sunday June 10, 2018.

Thanks to Emmauel Engelhart, @tim-moody and TK Kang who helped isolate the issue, which is a side-effect of kiwix-serve flag --urlRootLocation=/URL_ROOT

This is likely an accidental regression in kiwix-serve and Matthieu Gautier will work on it when he can:
kiwix/kiwix-tools#208