So, just to review the thread, the OP says that his phone appears to restart spontaneously and randomly, has anybody seen this? A number of people point out that there is a security setting that requires a passcode if Touch ID isn't used after a timeout, and you pointed out that this could also happen after 5 bad Touch ID attempts. But I answered, yes, I have seen this exact behavior, and it was a restart, because the message at the top of my phone said that Touch ID was disabled after a restart, but that I believe that it was caused after installing the app Dark Sky, because it stopped happening to me after uninstalling the app. The OP replies that he does have Dark Sky installed, but hasn't replied since to see if uninstalling it solved this problem.
Since the OP didn't mention that he had tried to use Touch ID 5 times, I think we can rule that out as a cause, with one possible exception - the phone's display lit up somehow in his pocket with the Touch ID facing toward his body and the Touch ID was able to get a capacitive touch through the material of the pocket 5 times and locked out Touch ID.
I only replied after your 5 bad attempts post because you said that you didn't see it as an issue. My phone was definitely restarting spontaneously, to a lock screen saying that it had restarted, without connectivity to WiFi - so, yes, it was an issue. Don't you agree, or is the phone spontaneously restarting not an issue for you?