Resolved! I'm using a LIS2DE12 for sensing the opening and closing of doors. 1) The chip is resetting randomly when I communicate with over I2C. 2) I need to trigger an interupt a deceleration (negative acceleration), but can't put in a negative thredshold.
The chip is powered by an 3v3 LDO. I have measured the output, and there are no fall-outs. I suspect my I2C adapter to be doing it. On-board the I2C is pulled up to 3v3 by 2k2 resistors. But on the adapter the I2C gets pulled up to 5V also by 2k2 res...