Vo2 Max

First try a restart:

Restart your Apple Watch - Apple Support

Unpair and erase your Apple Watch

Set up your Apple Watch

Sometimes you have to setup as new and not from backup since there may be some corruption in the backup that is causing the problem.

Possible Solutions for Vo2Max not recording

1.Tighten the watch band a touch and clean the sensors on the bottom of the watch..

2.Reset fitness calibration.

3.Input a VO2 max figure manually based off your last record from the health app then re-calibrate the watch.

4.Put the watch in airplane mode,do a walking/running or hiking workout of at least 20 minutes,when you've finished turn airplane mode off and let the watch sync the data to the phone.