We have had several electrical problems with both of our Chrysler’s over the years. I drive an Aspen, my husband the 300. A couple days ago his heated seat stopped working so he was like there’s another thing on the fritz. Well yesterday after getting out of work, his car wouldn’t unlock with the remote so he manually did it. When he opened the door, all smoke and soot was all over the front seats and his passenger seat was completely melted!!!!

 

I think that thing sitting on the seat may be why it burned

Blood flows thru the human body and carries away heat, that plastic would not, so the heat likely built up until the plastic caught fire.
If you look, the burns are only where that thing was sitting and you can see thru a hole perfectly good foam padding that would be blackened by fire and smoke if the fire started in the seat.
The issues with the power would be part of it, because those seats heaters do not normally work with the key in the off position, so that thing has a short somewhere that is feeding power to systems that normally do not have power unless the key is in the on position.

I'm not trying to defend Chrysler on this, just pointing out what I think likely happened.