In my experience with my local store, they will say that the dropping of the phone lead to the cracking of the screen as well as the internal effects you are having with it. They look for anything to get out of exchanging a handset at my local sprint shop.
I once took them an s3 that was having software issues, even after many factory resets. Instead of going ahead and replacing my device, with Mt insurance, she took the phone apart to look for water damage. The outside indicator was not showing water damage but the inside indicator was. So she said we had to file a claim. I argued with her about it, because that phone had never been dropped in water. Why would the outside indicator not show water damage but the inside show some? Anyway sprint did it right with the issue, but I'm just saying, they look for any reason not to exchange your device at no cost.
Sent from my Black Lg G3