It may be leaving the tube. It's happened to me but never saw it at this stage so it may not actually be exiting and I hope that's the case. But I did come home to see a worm that left being consumed by my orange plate coral (fungia app.$ ! I was too bummed to take a pic. Expensive meal.
They must do this because of stress - something about the location is wrong. Maybe fish nipping or flow that's not suitable. I never could tell for sure what flow rate was best for feathers or coco worms & haven't had long term success. I read they eat phyoplankton and need plenty of it. I have read and nelieve that they are not getting enough food, or the right sized planktonic food. It's weird that I have many of the little feather duster hitch hikers so you'd think there was enough food for filter feeders. I tried a few times over the years with others and 3-4 months was the longest they lasted for me. If I ever kept a NPS tank i will try again but I think I'm done for now unless I stumble upon a magic bullet somehow. I'd love dusters, coco worms and colorful sponges but that seems to be one of the hardest things to achieve.
I think you need to move yours to another location. Good luck & sorry for the pessimistic information.