You probably need to speak to DigitalOcean about this, we can’t support their one-click installs here. They’re billed as being simpler, and that may be true if they’re willing to support it, but we can’t.
The only supportable configuration is from the Standard Install Guide which will incidentally bypass all of the issues you’re mentioning above.
One caveat to note is that due to the nature of enrollment for Let’s Encrypt you can’t set a certificate back up without first repointing DNS. Let’s Encrypt needs to connect to your server by the DNS record specified.
Another thing to be aware of is that accessing Discourse by IP is totally unsupported.
I would recommend doing the standard install, that way we can at least help you with the process.