6x Pro Altimeter & barometer stopped working after last update

Have you tried to restart the watch long pressing the Light button until it reboots? You can also try to calibrate them after the restart to see if that solves the issue.

Yes, tried all of that with no improvement.... 

In that case, try a full factory reset and if that still doesn't work I would try to downgrade the firmware and the sensor hub to see if it helps.

If there is still no data you probably need to contact Garmin Support, it could be a hardware issue.

If it doesn't work after the factory reset then contact Garmin Support. It looks like you are the only one reporting a problem so it's unlikely to be related to the update. 

Ok, I did a 'hard reset'. All data and settings are gone. The barometer, altitude meter still doesn't work. However I see that the software update is still on 6.00. Any idea to do a reset on that one?

Up to you, but my suspicion is that you have a hardware issue with your watch. I would contact Garmin Support.