There is mention of "hooks" needed to correct for the workings of a Reverse Proxy, but after a long search one doesn't find a clear full example -- particularly for Nginx.
I operate Hypnotoad behind nginx, see Nginx in Mojolicious::Guides::Cookbook (in addition I do proxy_set_header X-Real-IP $remote_addr;, but that's optional). Plus, I had to set the proxy => 1 option in the Mojo::Server::Hypnotoad config, and set the MOJO_REVERSE_PROXY environment variable. (
The latter may no longer be necessary, I'm not sure because I worked out this config a while ago and Mojolicious evolves quickly, but it also can't hurt to turn it on. Update: I checked and AFAICT, in Hypnotoad, proxy=>1 sets Mojo::Server's reverse_proxy, but for other servers like morbo, it's the MOJO_REVERSE_PROXY environment variable. That's why I set both.)
Note that for requests that shouldn't be buffered/proxied, like EventSource streams, you additionally need to set the X-Accel-Buffering header: $c->res->headers->add('X-Accel-Buffering','no'); (docs).
However, the issue you describe may have nothing to do with the setup - the first step when things don't load is to look at the browser's development tools and the sever logs, or even a Wireshark trace.