FR24 also shows 3939 as having gone to MCI as just flight 9936 (not DL9936):
https://www.flightradar24.com/data/aircraft/n939dz

If I had to guess, 3939 went to MCI as both FR24 & FA list that flight. 3947 didn't, as not only does FA not show it at all, but when you "play" the flight back on FR24, it only shows the very beginning and very end of the "flight" when you would expect it to show the whole thing. But that is, of course, just an educated guess.