I personally would be concerned for a shock hazard. If it were just getting warm, ok...but shutting down, not so good. Samsung is a little more generous than most might think, I speak from experience. I say this, because I personally think you should make a support ticket and let them look at it.
Here's my 2 experiences with Samsung's support. Note 2 was 3 years old....caught fire while sitting on the counter. Called them and told them what happened, expressed with kindness, that I've been a die-hard samsung fan since the beginning of time (yeah, i stretched it a little) but basically, I won them over a loyal samsung-fan. They sent me a refurbished one at not cost to me.
Dropped my s6 active from about 3 feet to my concrete, hit perfect, killed touch screen immediately....called and said all the right things again...you guessed it, they replaced the screen at no cost. They told me that if it wasn't covered under warranty, they would not charge me, and that they would just mail it back to me.
Sorry for the long story, but its my opinion, to contact them and express your concern for a fire hazard "specific to mention, after the update!"
Now, you could.....research how to flash the original software through Odin, if that's possible with sprint...not sure.
Hope this helps!
Chris