What's happening to Elevation Gain accuracy?

I have been trying to figure out what settings in my APAC Enduro are causing elevation gains to be inconsistent. I have the following settings configured:

Data Recording: Every Second
Altimeter | Auto Cal. | During Activity: OFF | Not During Activity: OFF
Barometer | Watch Mode | Barometer instead of Auto

The first two times, there were no drastic changes in atmospheric pressure, it was either rainy or sunny during the entire hike. Then this morning's hike, there was sun and then a storm and I am beginning to wonder if Altimeter Auto Cal During Activity should be left ON instead. I have read from multiple posts that many have found Auto to be unrealiable therefore I turned it off and made sure I calibrate before each activity (using DEM if available, otherwise GPS)

Would love to hear your thoughts on this.