iPhone 6 overheating and causing the display to malfunction?

Ok, in December of 2015, I dropped my phone. Instead of cracking, the LCD stopped working and, a smell was being emitted from the phone. Still under warranty, I took it to apple and received a new phone. They said it was a software failure. Now, I have been using that phone ever since. Today, just about an hour ago, I had my phone in my pocket. I pulled it out to check the time but, it would not turn on. I immediately took it out of its case to get a closer look. I got a whiff of the same smell I had smelled almost a year and a half ago. I figured the worst. When I got home, I plugged it in and did a hard restart and, to my surprise, it turned on, thankfully. Now, I was wondering if anyone else has experienced this issue and, knows what it is. Thanks you.