After owning my Felix 5 for 3 years, I have figured out the issue (and a way to fix the issue) with the erratic pressure sensor.
After 6 months of ownership I researched the pressure sensor and learned that it is a capacitance-based sensor. I always had issues in the winter time and usually when wearing a jacket or long sleeve shirt, and when the relative humidity was very low (ie: indoors in heated buildings).
I determined the problem was static electricity buildup affecting the pressure sensor. I also determined that the watch was built like a capacitor with plastic sandwiched between two metal plates (the bezel and the back are metal).
To keep static charge from building up on the plastic mid section of the watch I placed a strip of metallic that touches both the side of the metal bezel and the side of the metal back piece. The strip is located where the two pressure sensor holes are between the two right-side buttons (I opened up holes in the strip for the sensor openings).
Since doing this the sensor worked very well (was not erratic).
The other day I noticed the metal tape has some green corrosion on it near where it touched the back metal. I removed the metallic strip and cleaned the watch but did not immediately replace the strip. Noticed the sensor was back to acting very erratic. This verified that the metallic tape does in fact prevent the static buildup on the pressure sensor that would cause sudden changes in altitude (ie going from 600 feet to 2500 feet in a few seconds).
Just installed a fresh strip ... and the sensor is back to normal again.
