What is going on is that the app is downloading the config and keeping it in memory but it is not saving the configuration in your device, forcing you to get a new code and sync every time you start the app.
There are 2 common causes for that, insufficient storage space or insufficient memory to execute the saving process.
To address the insufficient storage space, clean up your device, remove that not used widgets, apps and faces (use Garmin Express software in your computer, it is much faster than using the mobile phone), after that turn off and on the device.
For instructions on how to deal with insuficient memory take a look at this topic
Out of Memory Error
The online sync option serves to get the configuration from Genius Wrist web site and send it to your device.
Your saved activities are automatically sent to Garmin Connect and my app or site have no access to your activity. Sending information to garmin web site is an internal feature of your watch.
Be sure you can access www.geniuswrist.com from your mobile phone.
It took a long time but Garmin fixed this bug in firmware 2.80
Vívoactive HR is not activating (or incorrectly disabling) the optical heart rate sensor and also is not correctly reading data from other external sensors (bike speed/cadence or external heart rate).
This bug is in the watch firmware and it affects only NON NATIVE Garmin applications, that means all applications in Garmin Connect Store. It was detected in firmware 2.20 and persisted in firmware 2.30, 2.40 and 2.60.
I started a thread to discuss this at Garmin official forum and other software developers are confirming the same issue (Garmin Forum - vívoactive HR is not starting the optical sensor). While there is no firmware release to fix this, I will not enable the premium features for vívoactive HR devices.You already registered at Garmin Web Site, so you have a Garmin Forum account.
If when you try to register you see the message
Email 'your@email' is already taken
That means you already logged in the web site before.
The password recover and the resend mail confirmation only work for local accounts, if you registered with Gmail or Facebook you will have to use the same authentication provider to login. The forgot password feature or mail confirmation will not work in these cases.