It makes no sense for the detectives to lead a lengthy discussion with the medical examiner about how the victim might have received a fatal fentanyl overdose before the tox screen has even come back. At this stage they can't even know it was fentanyl or any other opioid. The observable symptoms are the same for any number of toxins, many of which are not even drugs.
It makes no sense for Dineen's addict girlfriend to leave all the money lying around that Dineen was literally rolling in prior to his death. The logical thing for her to do would have been to hide most or all of it even before any paramedics arrived, to stop the police from confiscating it.
It makes no sense for a Russian spy in the USA to have a thick Russian accent.