From the photos I can't be certain but, when I first looked at it I thought it could be a lamination issue.
A Die crack is when the Die itself cracks. When it strikes the blank planchet the metal flows into the crack making it appear as a raised issue on the coin. It does not cause to planchet to crack. If it doesn't appear raised then it could be a planchet issue such as a Lamination Crack. Looks like a Lamination to me.
Sweet, my first lamination error! I just had this nickel with a bunch of other old nickels in a roll I made a few years ago. Either I didn’t notice it or I just assumed it was damage. Thanks!