MAG2.(X/Y/Z) not changing in log. MAG/MAG3 is fine

I have PH2 with a here GPS/Compass module installed on my vehicle. It always works fine but in one of the flights I had this issue. MAG2.(X/Y/Z) has fixed value in the logs and is not changing with the orientation of the vehicle. MAG.(X/Y/Z) and MAG3.(X/Y/Z) are logged fine. After this flight the later flights were logged OK. I have no idea why this happened and was wondering if someone else has seen this issue. I am attaching a screen shot of the log. You can see MAG2.(X/Y/Z) is not changing and MAG.X is changing. I did not plot others so that the graph will not get cluttered. If you have an explanation for this then please share.