@tlrenkensebastian, here is a thread that I think shows a common issue (that we've been encountering for years) for Certbot users:
We'll have to see whether my diagnosis was correct, but the idea is that the Apache server has VirtualHost "stanzas" in its configuration, referring to the individual sites that a particular server machine serves (which can be numerous and distinct from each other).
Certbot's Apache integration is working with the assumption that the user has already successfully created a working HTTP (not HTTPS) VirtualHost for each site that will be secured by Certbot, so that certbot --apache will essentially find that VirtualHost and switch it over to HTTPS.
If users haven't done this prior to using Certbot, it will fail in some configurations and succeed in others. A particular challenge—most often under CentOS because it provides a "default" HTTPS setup with a non-publicly-trusted cert—is when people use the Apache "default" config without creating their own VirtualHost with a specified ServerName.
I think we already updated the Certbot documentation to mention this issue a couple of years ago, but it seems like people continue to have trouble with it.
That could be another important thing to put in the "preparing your site" documentation. In the draft I sent you before, I just wrote
This didn't really fully clarify what "get your site up and running with HTTP" means. 
(for example, that you should have a distinct VirtualHost, server block, or other configuration that refers to your domain name, even if only one site will be hosted on your server!!).