Ask HN: TN Visas denied for Canadian software engineers?

Last week I had an offer from a Bay Area startup for a software engineering role. As a Canadian, I thought this would be easy. Instead I watched in horror as me and two other Canadians in line at the Detroit land border got refused a TN visa. We were all given the same rehearsed "reason". The CBP officer quizzed us in detail about the nature of our job description, and then told us, in boilerplate words that seemed to be rehearsed, that she didn't believe our job description fit the role of "engineer" as defined by NAFTA, by repeating back to us some of the words we said in our interview. All of our documents were in order, however, and they acknowledged that. I got the feeling that they're trying to get rid of the TN visa, but in a plausibly deniable way, so as not to technically break the terms of the treaty with Canada. Think this may have to do something with renegotiated NAFTA?