Altimeter negative spiking after 17.50 upgrade, causing gigantic errors

Same problem.. started showing after the latest 17.5 sw upgrade

Same issue. Hike local nature center on a 4 mile trail with a total elevation gain of about 650 feet. After update altitude gain has been 24000+,24000+,17000+and 7000+ feet. It never was that great on that trail being 2-4 times actual but this is absurd to say the least. Hopefully this won't take months to fix.

Same for me sinds update to 17.50. After manual callibration at the start. Normaly the same track is mostly flat. Only few meters up and down.

I also have this issue or let's rather call it malfunction...

It began with SW 17.00 and even became worse with 17.50.

I spent now two evenings reading multiple threads dealing with this matter, however without finding a solutiion.

My last hope is to downgrade to SW 16.50, but I'm not able to find a repository which would offer the needed.gcd File.

Does anyboby of you guys have a Back-up of it and would be so kind to share it?

Remark: Correct measuring total ascent gain is one of my highest ranking expectations on such kind of wearables. If it is not working then the watch ist more or less useless for me.

Today I did another activity, starting from 1050 meter in fresh condition. First 15 km were downhill. As soon as climb started, this bug arised. I could see in the Instinct workout screen how altitude was spiking, even though climb was steady for some kilometers. I didn't begun to sweat when the bug first arised. So I don't know how to try to understand this failure, I first expected to be the infamous sensors bugged by sweat but with today's logs it doesn't seem to be the case.

At the end, what should have been about 1,100 total meter climb, resulted in 12,000+ measured by the Garmin Instinct. Hilarious!!

I attach screenshots from today's activity

This might "contribute" to the misreadings, however I doubt that this is really the root cause. 

In my case, it is quite obvious that these altimeter problems began with release of SW versions 17.xx. I never experienced huge deviations to the actual elevation gain with the previous versions before. And for sure, I didn't change the way of wearing my watch on my left arm (above the wrist). 

To me, it seems that the algorithm for this function has been changed and perhaps some "smoothing/filtering functions have been removed? For cycling & hiking activities, it should be quite obvious that such sharp drops are not part of the normal "moving pattern" and should be dismissed/ignored in the recorded data.

That's not the case. I have been wearing Forerunners for years and now the Instinct for a year, in the correct position. This issue is a device error, not user error. It all started with recent updates.

I have to agree with the observations regarding altitude gain. I just went on a trail run in very open terrain, starting 7AM and ending 8AM, so neither temperature nor pressure differences nor gps correction can be blamed (I did set altitude to barometer only in any case) and the result is abysmal.

Google Earth measure the effective altitude gain as 950 ft and this is very close to the readings I used to have with previous drivers. Today the Instinct showed 2186 ft.  I calibrated the altimeter before the run and post-run the altimeter reading was only 40 ft higher than the initial value, so the barometer essentially works just fine.

Under what conditions has the cumulative altitude gain function been tested? Has it ever been compared with older versions - pre-'improvement'?

As it stands now, elevation gain display really is completely useless.

In order to further narrow down this reason(s), I will simply wear the watch on my right arm on my next cycling ride. By doing this, the pressure port will point to the "backside" of the driving direction. If the elevation measurements will improve, then this would be a more or less acceptable workaround for me, even if I have to train my abilities to affix the watch with my left hand...