Uronema or Bump Injury or Other?

I’ve had a trio of Chromis for 3 months now, all eat well, swim together, but sometimes chase and nip at one another. In addition they have a habit of backing into holes where my royal gramma hangs out, where they will swiftly be chased away.

A red dot with a white center has appeared on one of their tails, that appears to be more pronounced on its left side but still visible on the right.

Is this early onset Uronema, a bite / bump injury, or something else?