Error 404 after signing up with email confirmation

I pulled the latest docker image with ca-certificates and other fixes, got an error after signing up. I filled in the registration information, clicked the button, and got redirected to https://comments.example.com/confirm-email, which returned a 404. I use Nginx as a reverse proxy, but I think (?) the 404 page is being returned by Commento, because it doesn't look like the typical Nginx error page. Commento isn't logging any errors visible from docker logs, but Nginx has this:

2018/08/08 16:38:56 [error] 22012#22012: *8247 connect() failed (111: Connection refused) while connecting to upstream, client: [REDACTED], server: comments.example.com, request: "GET /login HTTP/2.0", upstream: "http://127.0.0.1:8082/login", host: "comments.example.com"

Even though the 404 happened, I still received the "Confirm your email" email and was able to confirm my account and log in. So I'm not sure where this error occurred but I can help reproduce it if necessary.