Garmin Connect update rides but do not update statistics. Why?

henrik-johannesson said:

but the stats like VO2 etc. is not being updated!

Did the ride(s) meet the condition for a VO₂max detection?

My Recorded Activity Did Not Update the VO2 Max Estimate | Garmin Customer Support

• A power meter is required.
• Heart rate data must be recorded (from either a built-in optical heart rate sensor or from a chest strap).
• The Bike activity must be 20 minutes or longer without stopping.
• Your heart rate must be elevated to at least 70% of your maximum heart rate for at least 20 minutes continuously.

Yes, all the condition has been met in the rides

In that case, I recommend to Remove and Add a Device From the Garmin Connect App | Garmin Customer Support, then record a test activity, sync, and see whether it helped (it won't fix past data though). If not, then have a look at the Troubleshooting guide for (some) data missing after syncing for more tips. 

... you should also check whether the Edge 520 is set as your Primary Training Device.