GPS position drift or something else?

Firmware - ArduCopter-4.0.4
Hardware - Omnibusf4pro
GPS - Here+ RTK (but flying in 3D fix without RTK setup)
Build - 5" props quadcopter

Made multiple flights in guided mode which can be seen in the log below. In the first flight in guided mode, GPS position drifts to quite large extent, it should not be toilet bowling cause i have EK3_MAG_CAL set to 2 means quadcopter using simple heading fusion all the time. So i am confused who can be responsible for this drift, need help in diagnosing this large gps position drift which didn’t occured in next flights.


Please overlook roll & pitch oscillations as i was sending new position command at every 2 second intervals in guided mode.

your horizontal accuracy was about 71cm at this flight

in your log GPS_GNSS_MODE is 0 and its meaning that “Leave as currently configured”
try configure your GPS module to get best accuracy with this table

in my location i use 67 (GPS+GLONASS+SBAS)