Towards the end of the show, Jamie and his partner arrest the man accused of sexual assault in a restaurant and handcuff him. They never read him his rights. This is not a goof. Miranda Rights pertain to questioning. They have nothing to do with putting handcuffs on people or the actual arrest. The suspect was not asked any questions in the restaurant to require rights being read at that time. However, what is grossly inaccurate is having Jamie and his partner do the arrest in the first place.
Contrary to what Frank and Garrett discuss after Gallo is shot, attorney-client privilege does not end after an attorney quits. That said, that protection would not dissuade a mobster from ordering a hit on Gallo just for talking with Frank.