I had a similar issue with my Galaxy J3. I rarely drop my phone as it is in a silica gel case, but, from only an inch drop, if it landed on its back, it would restart.
I unclipped the back from the phone & found that the battery was a little looser than it ought to be & the rear cover didn't seem to be supporting the battery enough, so the battery temporarily disconnected if dropped.
I simply cut an inch square piece of plastic from a pop bottle, placed it on the battery, then clipped the rear cover back on. Problem solved, my phone has worked perfectly since.
It's worth a try & hope it works for you.