Resolved! LSM6DS33 WAKE_UP_SRC register not providing correct status data.
I have Pololu breakout containing a LSM6DS33 connected to a ESP32 module via I2C. INT1 is connected to GPIO15. I am driving Activity and Wake Up to INT1. The ESP32 picks up the interrupts reliably. I would like to know whether the LSM6DS33 is active ...