I spent some time looking into this and the issue seems to be that the discourse-narrative-bot blocks when fetching the avatar of the user to include on the certificate. Here:
This forum uses SSO and the avatars are Amazon S3 URLs — which are fast and not rate limited by Amazon. That said, that function is fetching an avatar URL of the form:
https://forum.tld/user_avatar/forum.tld/username/240/18705_2.png
Could the timeout errors that are slowing down the certificate generation be from hitting Discourse’s rate limiting somehow? Either by having the avatars being requested too fast from Discourse instance itself, or, from trying to hit Amazon S3 too fast when multiple users are doing the bot tutorial?