Is there any chance for Certbot nginx plug-in to support systemd start after a failed reload?
A major version seems a good time to make such changes 
If no changes could there be some additional messaging in the log or console to make clear the reload failed and the native command used to start nginx?
I reference this 1Y old thread but this recurs from time to time. The subtle "quirk" is also implicated in other cases where it is difficult to identify the cause of nginx state confusion.
As an aside, I wonder why Certbot even tries starting nginx after a failed reload. Couldn't it just issue a failure in such a case instead of trying to start nginx directly and causing problems on systemd systems?