I was kind of in harry (because was a break time)-and first time ever didn't do compass calibration,but like i mention i have flown here dozens of times. So I used previous calibration. I waited until screen showed safe to fly, home point was set up.
You dont need to do compass calibration if you're flying from same location man so I dont think thats it. Also from my understanding if it was compass fault its normally a matter of you giving it a command and it doing something else and so on.. in this case it was drifting so that does point to something else IMO.