Thanks for sharing this piece of data -- however, your oneliner is still working just fine there for me. I understand that you may not be in a position to share confidential data, but on the other hand, I'm sure you'll understand it's a bit difficult to diagnose a problem without a test case showing the problem.

I second what other monks have suggested: if regular expressions aren't working here for whatever reason, a proper XML wrangling module may be the way to go. And XML::Twig is specifically intended for working with very large XML files that don't fit into memory, so that's my recommendation as well.