I had 2 of them with coupler issues - One just hanging and had to re-assemble. The other the wiring broken off and had to replace the coupler. The other problems I had was one smoke unit didn't work (just push wires back in), the 2nd was one of the hatches on the B unit on top came off and had to re-glue.
They should have said - "Some assembly required" on the box.