Many thanks for sharing those two files with us, however when I inspect them, they appear identical to me. I even used a comparison tool to be sure, and couldn’t see any differences.
I did run your ORIGINAL.html file through a Manual test however, and noticed that your campaign is responsive on iPhone, however - as expected due to their lack of media query support - your campaign remains two column in clients like Android 5.1.0, Android Gmail and Gmail App iOS 7.
It also remains two column in iPad 2, iPad Mini and iPad Retina as well however, so just to confirm, were these the mobile devices you were experiencing issues with? If you wouldn’t mind confirming which specific mobile devices you were seeing problems in, we can investigate further : )
If it is iPad which you’re not seeing change to a one column layout however, then you may wish to perhaps try adding the below media query to your existing code, which should target iPad, specifically:
@media only screen
and (min-device-width : 768px)
and (max-device-width : 1024px)
So perhaps give that a try in the meantime and do let us know how you go!