Sorry to revisit this issue, but the game is still afoot, the error continues. Rather core or Simple:Press Plugins, “”An error occurred while updating xxxx.xxx download failed. Service unavailable.”
Event Espresso Premium had this same problem, and it was due a license key issue, where once the license key was reset, downloads commenced. The was true for another plugin I read about as well.
In the case of the Testimonials Premium plugin, it was discovered that WPEngine wasn’t using the domain download SSL, that caused the same error.
When GeneratePress Add-ons had this same error, the developers discovered it happening because the customer’s license keys are not properly activated on the URL that they have the plugin’s installed on it. Which can sometimes happen when a customer starts using the plugin on a temporary URL and then updates the URL to the final, live URL but does not change the license key to use the new URL. In some cases, the users had their email address deactivated, then subsequently activate the email address and all add-on’s and all updates worked thereafter.
Almost in every case, it was a licensing issue, which would explain why only a small contingency of users suffer this error. Thanks.