For the types I'm experienced in I have pretty good idea how this scenario can occur because I've either seen or committed some of the errors possible
- it might well help others if you shared this?
Easy:
Under ATC vertical control: level off here, descend there... so not in VNAV for the "approach" (PONAE) to the approach.
When established on final, set the MDA/DA (SOP-forgetting ATC said 1700ft...they did then say "cleared for the approach".) but still in VS: down you go all the way to the MDA, possibly before the FAF=bust 1700ft at DNNIS.