ISX won’t Regen properly

[tree98]

Did someone clean out the dpf with water or some other liquid? That's a BIG no no and can lead to the problem you're having.
Maybe the dpf is just worn out and needs replaced, do you take your dpf's to the dealer to have them baked and flow tested, or are you doing something else to clean them?
Could be you're doser isn't spraying properly and needs replaced. Have you done an EGR tuneup on it recently/ever ?
It would help to know the miles/hours on this engine.