I am doing some development work of some client software, so I use https://acme-staging.api.letsencrypt.org for testing purposes.
I got a fake certificate from your staging server. Perfect. So far, so good.
Then I shut down my server and ran my software again. I got another certificate! It appears to me that your server didn’t bother to challenge my server the second time.
Why should you issue a certificate to a server that is not even running, thus not able to satisfy your challenge?