It’s a issue with the over sampling with the PPK2 I always use the extra GND from the logic port to the GND of the chip(xiao), FWIW. Nordic forums has some topics about the PPK2, just lower the number of samples and go again.
Were you able to use a TILT interupt , if so how, did you write the registers directly? I guess too many Libs for the IMU, last count there’s at least 3. ?
Fun stuff… 
HTH
GL 