Then you have no way to debug.
What I would likely recommend is to spin up a new VM, install Discourse there, and restore a backup. When it works, put the existing site in read-only mode, backup, restore, and switch the DNS (or a static IP if you have access to such).
You can use Move a Discourse site to another VPS with rsync so that the new site has valid certs and you can have a look by hacking your local DNS to point to the new IP address.