Just had the same experience as the OP, my Girlfriend's Samsung Galaxy s6 phone, while on vacation, in a no service area, with over 500 yet-to-be backed up irreplaceable photos, seemed to spontaneously perform a hard reset while she was placing it in a stupid selfie stick. After reading through the above posts, I want to add what I have found.
She didn't have any password on the lock screen, so there should not have been any 15 attempts to open.
Though the volume and the power button may have been pressed while installing it on the selfie stick, the home button was not.
The firmware version, G920VVRU2AOF1, is presently un-rooted, so the normal ways to root and recover data are not available. PingPong's root system is dependent on Chainfire and they have not rooted this variant. Odin doesn't seem to be able to be used to rollback the firsware version to a root-able one. I also could not get my computers to view the phone as a lettered drive so I could use my usual data recovery tools on it. Verizon Tech support was utterly useless and a waste of time.
It is beyond unacceptable that Verizon/Samsung could put out a phone with no removable memory that can accidentally perform a hard reset during normal use of phone with no password protection that wipes out all of the irreplaceable data on the phone....with no way to recover it. They can and should do better than that.