The phone calls mean very little. A lot of the times Tier 1 agents make things up to get callers off the phone.
USCIS mistakenly denies cases from time to time. USCIS mistakenly issues documents and even naturalizes people, which sometimes gets discovered and reverted, other times not.
I understand your frustration with my seemingly pointless questions, but I'm trying to get some clues as to what could be holding it up. Is the immigrant admissible into the US? Did you ask the lawyers what could be the reason?
You may want to file FOIA to get all the details of the case.
Sorry if I'm being repetitive. What's the actual case status right now as you check it by case number here?
https://egov.uscis.gov/