I’m having similar issues. It can be stable for weeks and then jump from ~50m asl to 4000m while dropping temp to -50C.
E.g last week it was nice and stable (ski touring, alt. scale on the right, both profile and 1000-2000m range are correct):
[image: 1582731632615-7dedde5f-0df4-4b7b-8dea-96881dc3d73b-image.png]
A flat run back home few days later, real alt. diff should be in 10-15m range and it’s generally ~50m asl; bit challenging weather and trails in the woods, so some fused-alti shenanigans and baro drift is kind of expected:
[image: 1582732395125-9b5c3cca-1da0-4997-9f38-3689d97c2888-image.png]
And then this last night, real alt. diff should be in 30m range instead of 4000m. And when something like this happens, I always tend to get those choppy alt. charts in TP. Adjusted altitude before heading out but but it was rising from 50m to 1000m in like 5-10 minutes.
[image: 1582732130510-ce72c871-92ad-487c-9271-af5863497829-image.png]
After that last run I soaked my A3P in warm water for an hour or so, turned off fused alti, reset gps,switched to baro mode and set ref. altitude. And it has been super-stable for past 20 hours. Last time it did something similar was about a month ago.
On a good day I still get something like this from my A3P for ~30m alt diff runs and this is almost identical of what I would get from 1m resolution DEM data provided by local land survey:
[image: 1582733606716-8865ad9b-8837-49e3-8b41-00d2d8ef0a68-image.png]
