Just to be clear, I have seen a couple other posts in the last month that involved a "Service busy" message
Though I think there were generally other issues involved in those cases too, it may be that "Service busy" is happening more often than it used to. But agreed that most users are getting certs fine, and even if one attempt isn't working then the next attempt generally would. And I think the most common clients may be retrying automatically (as they should) rather than informing the user, so most people might not notice even if the message was happening more often to them.