Catalytic converter?

My wifes escape had a plugged converter off manifold. The car has 3 I believe. The shop replaced the second converter in line stating that the one nearest the manifold had blown out and had plugged the second one. They said the one nearest the manifold was completely open. Ever since the work was done my wife's car has a slight chugg or jerking when she stops at a light or stop sign. Is this a lack of back pressure due to the one missing converter or what could it be?