I found that LAContext's method
- (void)evaluatePolicy:(LAPolicy)policy
localizedReason:(NSString *)localizedReason
reply:(void(^)(BOOL success, NSError *error))reply;
the reply block's error will return some error code that is not in documentation.
Such as -1000, Pending UI mechanism already set.
This error be fixed by relanuch the device. but what kind of informatino we can give to end user ?