I've just remembered one "difference" between the two devices: Their "typical" supply voltage.
The LSM has supply specs of 1.71V (min), 1.8V (typ), 3.6V (max). The BMI has supply specs of 1.71V (min), 3.0V (typ), and 3.6V (max). We run both parts on a 2V5 rail that was already in this board's previous design. I personally contacted both vendors and asked them if their 1V8/3V0 was actually preferred, or if 2V5 (which is obviously well within both device's specs) had any disadvantages compared to their "typical" supply voltage value. Both companies replied and explicitly said that 2V5 was perfectly fine and that voltage had no disadvantage compared to the "typical" values they listed in their spec sheets.
I don't think that could cause this LSM problem, but I did notice it and got the manufacturer's opinion before committing. That said, 2V5 isn't their "typical" value for either part and is 50% higher than the LSM's "typical" while still comfortably within its acceptable range.
Just tossing that out there in case it rings a bell for anyone. Again, I can't imagine how a part would stop locking up after it "grew accustomed" to a different supply voltage....
