^macduke, thanks. That is very interesting. Adding that one to the list.
The A9 chip theory
Not to get suspicious yet but the poll so far has 100 samples and has almost an exact 40:60 ratio of people who experienced this issue to people who haven't. Guess what else has a 40:60 ratio? Samsung to TSMC A9 chips.
See for yourself.
This theory is flawed because A) not everyone who took the poll has a 6S B) unlikely Apple didn't test the chips to such a poor failure rate C) 6's and and some 5's have the issue, although we lack data still.
Anyways, we just need more information. I am updating a public file soon to aggregate everyone's data.