Hi, I am the Bosch FAE located in Sunnyvale, CA. I will contact you directly through email.
The BMM150 X-axis data overflow or saturation may be caused by the decoupling capacitor that is placed near X-axis coil of BMM150 on the PCB. That capacitor may have ferrous material such as nickel inside. If you change to another kind of the capacitor, then the X-axis overflow issue may be gone.
That was the issue - confirmed now. The capacitor near the magnetometer was a Murata part that had nickel plates. The down rev board used the same cap value but was a TDK part with copper plates. Switching the capacitor eliminated the overflow issue. Thanks!