Hi schlecns,
After review your schematic, BHI360's VDDIO can only be powered by 1.8V and cannot be powered by 3.3V, ensuring. We suggest using 1.8V power supply for both the VDD and VDDIO domains of BHI360 and BMM350. We suggest that you use a logic analyzer to capture SPI communication waveforms and check the actual communication waveform situation.
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