Your compass is junk. Well, maybe not complete junk, but it is one of the most delicate sensors on your drone and is prone to interference. It is important to keep compasses away from any potential interfering magnetic fields. Cables carrying large currents and motors are prime sources of magnetic fields. Also, be careful about the location of any ferrous metal, especially if it can move. Interchangeable batteries and cameras will affect the compass calibration each time you change batteries or camera. To make things worse, stabilized cameras have motors.
The compass’s alignment with respect to your autopilot’s gyros and accelerometers is also important. Small errors in alignment between the compass and gyros can lead to heading errors. Heading errors directly impact a hovering vehicle’s position holding ability.