I\'m dealing with a third party PHP library that I can\'t edit, and it\'s been working fine for almost a year. It uses simplexml_load_string on the response fro
Your XML is Invalid and should cause an issue in both cases.
You need to have ONLY ONE ROOT.
ie. Everything should be inside your tags:
...
You have multiple roots in your XML, which will cause an issue :-)
Try wrapping it all in a root node and see if it works.
...
I'm not sure if it would be the difference in libxml, or a different level of error reporting allowing it to work on one and not the other, but that looks like the issue to me.