The SSL certificate for our wildcard domain had expired. Forums with custom domains aren't affected by this, as these are automatically managed by Caddy. But since I haven't provided the Cloudflare API key, a wildcard domain certificate can't currently be provisioned by Caddy.
I am currently not at home, but I will try to see if I can push some fix right now. If not, you'll have to unfortunately wait for a little longer. I apologize for the inconvenience.