Elevation data - Lack of.

Hate to say it, but your watch is broke.  Had the same thing happen to me last year and the only fix was a replacement watch.  This seems to be a rare break, as I couldn't find any similar cases when I was browsing the Garmin forum or other sites. 

If I recall, you can do a full reset or an update and your altimeter will work for ONE activity, and then it will break again once you do one more.  I repeated this cycle of doing factory reset before an activity, and eventually even that workaround stopped working after maybe 5-6 factory resets.

Had to have the watch replaced by Garmin.  This was on a 6X Pro Sapphire.  I also believe mine broke after an update.

Cheers for the reply although not what I wanted to hear for sure. 

Haven't had a chance to do anything yet other than a walk in the ark with the dog and indeed exactly the same behaviour. 

Curiously it seems something is happening. My starting elevation was 270ft after doing a calibration and it remained that for the entirety of the walk as I watched it on the elevation data screen however between finishing the activity and arriving back home the elevation was now -146ft. 

So the park and my home address are indeed on different elevations but not to that degree!

The point you make about update possibly 'breaking' the altimeter is interesting. 

Like my OP stated it worked in-between updates but I was to of action with a broken elbow at that point so was really using the watch and by the time I have reached the stage I am at now several more updates have come along and now I am in the situation I am. 

I will do a reset shortly and test tomorrow and see if I also manage the one activity and back to square one you experienced and then contact support. 

I may as well do the reset first as I imagine I will be asked to first anyway. 

Out of interest did you have to pay full price for your replacement?

I will be a tad annoyed having to fork out a lot for something that has possible been bricked by an update. 

Well a full reset last night has made no difference. 

Altitude is all over the place and a quick test walk which I know from previous use has enough elevation change for the watch to react to gave me a 0 total again. 

Have reached out to support. See what happens going forward. 

Just had a quick look back over my data and it appears the problem started back in October not December. 

However on occasion it would start to work again before once again ‘failing’. 

Common denominator in all of this. Every time it stopped or indeed briefly started to work again it always coincided with a firmware change. Make of that what you will but the shear number of updates we have seen I am wondering if one of them is the culprit in my case. 

Anyway. It will be what it will be now once I get contact from support. 

There are some holes in the side of the watch case which must be open for the altimeter/barometer to work properly.  Check if these are blocked

This makes sense.  Also and also what happened to me.

I would double check that your altimeter is actually working.  If I recall, when I started an activity it would lock a new altitude using GPS (not baro), give me 0 change on the activity, and then stay at that altitude until the next activity.

Also, check your barometer.  Does it read "----"  If so, that was the death knell that eventually my watch could never recover from.

I was probably about 2-3 months outside of warranty, and Garmin did take care of me.  However, I did send them evidence in my troubleshooting that indicated the problem began during the warranty period.  I am not sure if that was a factor in their decision - it didn't seem so.

Ports are clear as much as able to tell. I don’t think it’s that tbh but worth mentioning especially as someone else may find that to be their issue. 

Well rather annoyingly I’m about 10 days out of warranty but having gone back through my training history the issue I would say clearly start in October last year which would definitely been inside warranty had I noticed. I then broke my elbow meaning two months passed before starting to use it again. 

I would like to hope if it has indeed failed that Garmin will be fair. Even without the obvious signs it was going back in October, 10 days out of warranty is nothing really and whilst yes, we get a 24m warranty I’d expect much longer life from something costing as much as they did at the time. 

As for the Barometer. Yes. Often gives no value. Once I recalibrate or soft reset it’ll kick back in though but like the Altimeter it rarely changes. 

Have noticed that since getting home earlier my altitude has increased from 82m/270ft which is about right to 118/387ft which isn’t. 
Prior to hard resetting last night it would go the opposite direction and have me sinking rather than floating away!

Definitely something has gone a miss with the sensor(s).