Please read the error message again. The update site that Joomla cannot open is called "XT Adaptive Images" and the URL it cannot open is http://cdn.extly.com/update-xt-adaptive-images-pro/extension.xml. This extension comes from Extly which has absolutely nothing to do with Akeeba Backup or Akeeba Ltd.
I can also see that the URL is accessible. Most likely your server had a temporary network issue which has now been resolved.
Sorry, I will have to close this ticket as out of scope.
Nicholas K. Dionysopoulos
Lead Developer and Director
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