RP, I had that happened to me in a couple occasions, one was traced to CA glue the other I never knew. I am not a segment turner, but an area of a bowl finished bright with epoxy, as per directions of the person that order it. I always put my bowls in a vacuum pump, if they hold vacuum they get walnut oil finish. That bowl was a heavily patterned spalted red maple and it did not hold vacuum, so in close examination I spoted an area punky, and that got the CA glue next day I sanded the whole thing and a layer of low viscosity epoxy was applied, the whole bowl was shinny and a very dull spot where the CA glue was. The client refused to take it.