iPhone 6 Plus weird, random UI/screen bug

Hi, ever since first getting my iPhone 6 Plus 64GB back in November, I've been getting this random issue (happens a few times a week) where without even touching the screen, the entire UI of iOS will quickly move down to the vertical 50% mark of the phone's screen. I've found the only 2 ways to fix this and get the top of iOS to be realigned with the top of the phone's screen is to either press the phone's home button or lock and unlock the phone using the lock button. Anyone else here ever experienced this issue with their iPhone 6/Plus? How did you fix it? Was it a hardware or software issue? Thanks