After calibrating the barometer the trending arrow is pointing down 15min after every altimeter calibration

Hi. My fenix 5x plus was showing 8mbar above the reading of weather station in my area. I did a manual calibration of the barometer to make it match the correct readings. First the trending arrow is flat, but after 10 - 15min the trending arrow is pointing down after calibrating the altimeter. Every time, even if the pressure is stable. 

I have attached two pictures to show the problem.

This is an old bug witch was present on my fenix 5x, the solution then was do a factory reset. I do not want to do that. 

If there is a solution, please let me know.

Best regards