Maybe not fully serviced? Has it been dropped? What do you mean by "A few passes thru the demagnetiser"? Have you demagnetised the watch correctly? https://www.youtube.com/watch?v=-ODu91ZUeVI
Full service 2 yrs back thru GP at a cost of £700.
Sparingly worn since - never dropped it.
Used the video as a reference point. Also did it 3 times - doesnt move the compass needle now.