The problem is Pentaho uses the "Java flavor" of regex, I use regex101 myself when I need to text my regex because not having much knowledge of regex, is very useful with the explanation and cheatsheet, but sometimes there are some quirks specifically for java you'll need to modify.
Unfortunately I can't help you more, but I would look for some java specific forums to try to decode what it's not working there.
A suggestion, I wasn't able to open your ktr because there are a bunch of master-slave details and connections needing a specific jar to open it, I had to clean that information with a text editor to open it. Besides, your Text Output step had the path hardcoded, it's better to use the ${Internal.Entry.Current.Directory} variable to generate the file in the same directory where your ktr file is when you are uploading examples.
Regards