Loiter mode oscillates

Hello community, I have a issue in loiter mode in my hexacopter while flying in stabilized, althold mode the drone is flying stable but in loiter mode for first few seconds every thing is ok but after some times the drone starts oscillates towards front and back, gps connections and hdop values are good securely mounted top of drone and gps faces towards front. i did the calibration very well, even i checked telemetry data, logs even i monitored system screen but there is no issue but the drone oscillates in loiter mode even i changed the gps tooo still same issue. kindly help me to resolve this issue.

Your PIDs are not correctly tuned. Use Ardupilot methodic configurator software to semi-automatically tune it.
Make sure to read and follow the software instructions, otherwise it will not work.

Thanks for the quick response, a month ago one person instructed the same but I’m not sure about how to work in it so dint complete that process, exactly i don’t know how to complete it soo. sir, could u pls give some detailed explanation or guide it will really help full to achieve in my career.

The step-by-step details are all in the document that I linked to.
That is the explanation or guide.
Have you read it?

If yes, post concrete, to the point questions.