I was not able to reproduce the issue. You are using Bitnami Discourse AWS Cloud image, right? Could you check the
Signup email template?
Moreover, could you access your rails console to check if the
base_url variable contains the port or not?
RAILS_ENV=production bundle exec rails console
Inside the console, put this
Which is the
url that appears? Does it have the port?
Hope it helps.
Javier J. Salmerón