Started out a test flight in my yard - a place where I have flown dozens of times before and, IIRC, the last place I calibrated the compass. I checked my compass MOD value - 1530, which is typical and had green everywhere. Did not recalibrate. As I got to about 50 feet I noticed the back LEDs blinking yellow. Looked at the screen and the app complained of 'COMPASS ERROR'. I put in in hover and noticed it was wandering back and forth - to be expected with a compass error. So then I started bringing it back. This was an exercise in manual flight since this part of my yard has a bunch of trees and a deck. I purposely fly here to practice control for landing on the boat. But I had a heck of time herking it in - it wandered back and forth, should have switched to ATTI mode but then the LEDs went green and she behaved normally. Did a giant slug of iron magma just burrow under my house or is this a typical error?