It may be an issue with EMI (electromagnetic interference). The Compass is located on the underside of the rear window shelf. Are any of the newly installed stereo components in close proximity to the compass?
Since your stereo install how have you been reseting the compass? Just pushing the reset button? FYI In the manual it tells you to drive in small slow circles right after you reset it with the correct zone #. After I did this my compass works correctly, This also happened to me after my stereo install, cause the battery got disconected.
i am driving in circles. how do you pick the correct zone. maybe that is it. sometime it will work and some time it won't. then all the sudden it will go from not working needing reset to working. i don't get it