Union members in one of the state’s largest school districts aired grievances about a deadlock in contract negotiations during a tense board meeting Thursday, with at least one educator announcing her resignation amid the bitter dispute. More than a half dozen employees in Elizabeth Public Schools expressed frustration with conditions in the city’s 27,000-student school district, saying during the meeting that pay raises proposed by the Union County school district did not go far enough. Among those who spoke were longtime teachers, counselors, and secretaries of the district. “Morale is at an…