That is very common. Let it be, and eventually it will dry out. Meanwhile, other roots are forming, making up for the loss of this one. If you attempt to disturb the mix at this point, it will likely end up with a lot of root damage.
Here is about the time I transfer out of the clear cup. I had at least 2 long root shoots do just like yours is doing. If you look at the bottom left of the 1st pic, you will see a dried up root from awhile back. No ill affects after it dried up.
