Altimeter inaccuracy

In my case barometer/altimeter is a sad joke as well.
Weirdly problem occurred or ridiculously escalated like 3 weeks ago, after around 7 months of using the watch.
It's completely random. Half of the times it's reasonable, half not even close.

Todays run on a relatively flat surface, easy forest trail. Expected +/-30m elevation. Watch recorded 238m up, 250m down. Useless.


Bike rides sometimes are much more absurd. 
4km ride along the road in the city. Google says 5m up. Watch registered 764m up...


Watch 955 Solar.
Current FW version: 19.13.

I'll probably wait for two or three next firmwares. In case of no changes I'll try to ask my local support for 'advice'.

Thanks for the tip! Unfortunately 2 hours soppy bath didn't help. At this point it cannot be more useless. Except ludicrous stats during activities, I also for instance instantly gained 100m of elevation at 4 am while sleeping and my floor counter skyrocketed.  

Quite a few users reported that it appears to get worse with cold weather. In my case, I think I figured it out, it is not the cold weather. Rather, the altimeter issue presents itself in cold weather, not because it is cold, but because of the sudden temperature changes. In cold weather, before you leave the house, it will be warmer inside than outside (well, at least it is at my place). It could be that the watch takes a good 20 minutes to drop to the outside temperature. Most people would leave the house and start jogging or bike riding pretty much right after leaving the house. When the watch starts to detect the temperature drop, and it happens during the run, it attributes it to the altitude change, so you end up with ridiculous readings like the 5 k run I did below. Note that the altitude change follows the temperature change sometime after it registers. The 5k run below is a return trip, so the second half should be the mirror version.

So, next time, I left the watch for 30 minutes outside before going for a run, and this is the result (on the same route).

As someone looking at a 955 because the altimeter is busted on my 935, I'm blown away Garmin still hasn't fixed this.

 I waited 23 months to send the watch for assistance hoping that with a new firmware the problem would be solved. The watch was replaced with a new one, not refurbished but new. Mine was rev A this rev. C. The altimeter of the new one is of impressive precision so the problem was hardware. To easily understand if your sensor is broken I recommend you do this simple test: calibrate the altimeter and stay in the same place for at least 4 hours, if the altitude does not change the sensor is ok but if it is not constant the sensor is broken 

 I waited 23 months to send the watch for assistance hoping that with a new firmware the problem would be solved. The watch was replaced with a new one, not refurbished but new. Mine was rev A this rev. C. The altimeter of the new one is of impressive precision so the problem was hardware. To easily understand if your sensor is broken I recommend you do this simple test: calibrate the altimeter and stay in the same place for at least 4 hours, if the altitude does not change the sensor is ok but if it is not constant the sensor is broken 

 The rev is on the box. Attached are the old and new boxes. However I have a friend with rev A that works perfectly.  

I got an A back aswell.

Not to much problems as of yet, but I am not wearing it under the shower and in water (sea/Pool) anymore.