Well, I had a weird experience over the weekend with the App. My KTN was being stripped from the boarding pass when I added it to Apple Wallet. Of course, I didn't bother scrutinizing it and just went right through Precheck until the agent said I didn't have Precheck on my boarding pass. He was right. Oddly, the boarding pass in the Alaska app did show I was Precheck. I tried a few different workarounds and none worked (deleting and re-adding, inputing my KTN number into app again, and killing the app and opening it again).
Just an FYI for others that like to add boarding passes to Apple Wallet. Check to make sure your Precheck status is on there.