IME, new heads on a Duncan, will sprout up at the base of the head/polyp. Not saying they don’t sprout up anywhere else on the branch, they just never have on mine. A clearer picture will help immensely
I hope that's a new stem, which would be awesome. It has never happened to mine. But if you worry it's something bad, you could do a bayer dip. Duncans are pretty good at handling bayer.