The Third Circuit has confirmed that a petitioner seeking cancellation of removal (a discretionary form of relief) still has a Fifth Amendment right to due process, including effective assistance of counsel. Thus, even an applicant for discretionary relief may assert an ineffective assistance of counsel claim, which is reviewable by the federal appellate court.
The full text of Calderon-Rojas v. Attorney General can be found here:
https://www2.ca3.uscourts.gov/opinarch/192332p.pdf