Same here.
/ work good.
When move behind /test on my reverse proxy and add custom_base_url : "/test" i can't load css/js/png...
I tried with/without option reverse_proxy_setup: true/false

In final case i would like if possible to rewrite-target on my proxy (so i'm suppose to set empty custom_base_url ?) but this do not work because sources URL generated seams absolute (i made sure that absolute_urls: false).

Here is my config for final case :

home:
  alias: '/home'
  hide_in_urls: false
absolute_urls: false
timezone: ''
default_locale:
param_sep: ':'
wrapped_site: true
reverse_proxy_setup: true
force_ssl: false
force_lowercase_urls: true
custom_base_url: ''
username_regex: '^[a-z0-9_-]{3,16}$'
pwd_regex: '(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).{8,}'
intl_enabled: true

http_x_forwarded:
  protocol: false
  host: false
  port: false
  ip: false

This is what i expect:

<link href="user/plugins/markdown-notices/assets/notices.css" type="text/css" rel="stylesheet">

This is what i have:

<link href="/user/plugins/markdown-notices/assets/notices.css" type="text/css" rel="stylesheet">

It seams like if custom_base_url is empty assets are loaded with a / which is an absulote URL ?

I'm not a PHP expert but i don't think we should add rootURL on relative URI here ...