I am facing the same issue.
If served directly by Haproxy, it works.
If served Haproxy > Nginx, it doesn’t work.
Did everything by Strapi docs.
It can’t find anything under /admin. Nginx screams File Not Found in /etc/nginx/html/… .js
This way it can’t find robots.txt either
I tried to set the root path in Nginx to /path/to/public.
This way it found robots.txt, and responds to /, but nothing else.