Help . gps moves constantly

help. drone position moves constantly in the planner mission map, the drone being in a fixed position.

shows a purple color tracking line

I have an apm 2.8 and gps ublox 7m

Standard GPS has a precision of „only“ ~5m (exact accuracy depends on #of satelites, atmospheric conditions etc.) so it is quite normal that you see some movement on the map even while on the ground and stationary.

Totally normal. Static GPS position is dependent on the number of satellites AND the received signal strength from each satellite. The “birds” are not in stationary (geosynchronous) orbits, so the actual satellites being “seen” may change, but typically the number of satellites being used will remain fairly constant.
Additionally when the aircraft is not airborne and moving, the navigational algorithm does not have all of the data it needs to navigate, so the displayed position will drift. Once the aircraft has taken off and is flying the accuracy of the displayed position will become more accurate.

So, as long as the APM has a 3D lock it is safe to arm the motors and take off…