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Hi guys,
I will just paste my answer here for you ok?
Well I had got the same issue. After researches and call to Prestashop Support, I have not found any solution for this issue ... but I always kept in mind this is a host issue.
Well finally I found the solution and I hope this fix your issue too. On my web host exist an option "page speed optimization", this is a new feature from "google"(https://developers.google.com/speed/pagespeed/) to improve ours website links, but this specific solution doesn't work fine with "XML". XML is a much stricter language and does not handle "page speed optimization" well. Explaining better "page speed optimization" does is it removes repeating or redundant code from URLs. Though XML is looking for the complete URL and fails when it does not find it.
I hope this solution help you to fix your issue.
Greetings.