Dear Droners :)
Every thing was OK, copter stays in loiter mode without any problem.
After slight modification, added FPV TX, OSD and LC Filters and Gimbal cpter is flaying away in loiter mode. It looks like it change position very aggressively. GPS is NEO M8N module based.
When it stays on the ground (balcony) position is not stable, i changes within few meters.
I've seen also hat after powering up copter and after GPS is fixed I've armed a copter and for one second I've seen no GPS Fix, it also is in the logs. In logs there are some Errors EKF and no exact time. Year is 1979 .... strange. Look like GPS is not fixing a time ?
I've did also some GPS module configuration, file from Ardupilot Wiki.
FC is PIXHAWK and Arducopter 3.3.3.
Of course, compass calibration was done.
Any ideas, module is broken somehow or there some interferes of power issues.
I've no idea at this moment :)