Correct me if I'm wrong, but isn't it also possible to just use one of your fingers that you didn't register with touch ID for 5 or so consecutive unlock attempts and it will have the same effect as rebooting your phone?
Keychain and NSFileManager have possible modes of "kSecAttrAccessibleAfterFirstUnlock" [0] and "NSFileProtectionCompleteUntilFirstUserAuthentication" [1] respectively that are (fittingly) in an open state within your app after you've unlocked the device.
[0]: https://developer.apple.com/reference/security/ksecattracces...
[1]: https://developer.apple.com/reference/foundation/nsfilemanag...
As an aside, I've found that, at least with my iPhone 5S, if my finger is wet (e.g. if I've licked it), it also is rejected.