Failure and data loss using transferUserInfo method on watchOS 2

Question

When Apple Watch and iPhone are not in range, I am sending 5-10 data dictionaries through transferUserInfo and observed that all dictionaries got delivered successfully when the devices come in range within 10 minutes. However, if I bring the Apple Watch in range after 15-30 minutes, I observed that few records got failed.

There are few records for which I got acknowledgement as success (didFinishUserInfoTransfer) on Apple Watch, but didn’t reach the iPhone. Is it something to do with WCSession getting inactive?

if ([WCSession defaultSession].isReachable) {
     [[WCSession defaultSession] sendMessage:userInfo
                               replyHandler:^(NSDictionary<NSString *,id> * _Nonnull replyMessage) {

                               } errorHandler:^(NSError * _Nonnull error) {

                               }];
} else {
    [[WCSession defaultSession] transferUserInfo:userInfo];
}

I have activated the session in applicationDidFinishLaunching of my watchOS 2 app.