Well, no, but I'd bet that it's the cause of your problem.
They're really all rooted in Let's Encrypt servers being overloaded.
I think this is because the authorization objects being used weren't replicated between their servers fast enough between the request your client made (on one server) and the operation the client attempted to do on it (which hit another server in their cluster). (They call it "the 404 bug".)
This is really just another "Service Unavailable" error (503), just from a different part of the process.