Problems with snow tire cables

Getting this from Mrs Cad in the Springs while I’m in PHX so I have her description to go on.

Seems like she put on the cables pretty quickly on only her second attempt. (I’m worried because it’s a biotch to get the back fastener on on her MustangGT). The chains work fine but the Pony did not have enough clearance to get over the snow between the tire tracks. She then tried to rock it off going back and forth (how many times I don’t know) until she got a push out.

But in the meanwhile BOTH chains apparently failed and wrapped themselves around the axle. Two questions:

What probably caused the failure? I think they may not have been on tight enough. But then why would they come off only when she started to rock? Beside she knows 3 notches in the back and 4 in the front (tire perspective) to get the cables on. And if it were a true cable failure, would BOTH have failed simultaneously?

Easiest way to get them off? Since they are on the drive wheels, one could jack it up and put the car into neutral to help unwind, but that sounds like a recipe for ending up with the GT as a tight fitting hat. Does she just have to crawl under there and unwind them the hard way?