UPDATE... After restarting many, many times, the "Unable to determine if your iPhone display is a genuine Apple part" alert was persistent. Prior to that, I only saw it one time and then it went away. Coincidentally, I didn't experience the touch screen issues for over a day, which was the longest I've observed. I don't know if having that message appear and the touch screen issue seeming to get better are related.
I ended up taking it to the Apple store. My phone is only a few weeks old. Given that I had that alert message, they were able to quickly move forward with a screen replacement, which I did. The phone is under warranty so the screen replacement was free. It was all very straight forward and the ultimate diagnosis was a bad screen from a manufacturer defect.
The Apple tech said that if I would have bought my phone from the Apple store, they could have just swapped the phone if that's what I desired b/c it was so new. I got a deal from my mobile carrier when I bought the phone so that wasn't an option. Just an FYI.
So in summary, I don't know if the touch screen freezing error is ultimately related to the 17.3.1. Maybe it is but it does seem like a hardware issue. New screen is working fine and the iOS alert has gone away.