GPS Cal Failing

I have three planes all with identical firmware and parameters that are not completing there GPS calibration it gets to about 86% every time then beeps to let me know the Cal has stopped. I have done a total of 8 machines to day. The strange thing is they will complete every time if i’m inside but not if i go outside to do the Cal correctly. I have repushed Firmware, and updated the bootloader as well as reseting parameters to default. with sadly no change. any ideas because i am out of them.

1, you calibrate compass, not GPS.
2. If it works indoors then there is some magnetic interference at the location where you do the calibration. Where did you tried it ? Any metal structure, reinforced structures, fence etc… ?