Many times, if it looks like it broke at the nut, it really broke at the tuning peg because of the stretching involved. I had to get a peg filed to take out any small burrs on my Pono. After that, all was good... until the bridge moved a little and threw the intonation off at the higher frets, but that's another story. Oh, and the A string's action was too low, but a piece of toilet paper fixed that in a jiffy. Oh, and the frets were too sharp and would catch my nail from time to time, but I had it filed. Oh, and my warranty's probably void now for "unauthorized repairs." Oops. *sigh* the woahs of a pricey uke needing repairs.
Anyway, back to my point... either you got a small burr(s) somewhere cutting the string or the string's quality is subpar. If everyone's getting the same issue from the same string manufacturer, we could write to them and let them know something is wrong.