Model: A1688 iPhone 6s
Storage: 128GB (55GB free space)
Nothing special about the phone, not jail broken, it has a fair amount of apps, but plenty of free space.
I also tried a fresh reboot of the phone and reran the sample app and still had the bug.
A colleague is also experiencing the problem. (I believe he has an iPhone 6+ with 9.3.1)
Let me know if you want me to run any more tests or need more information about my device.