Hi Barry,
What you say is make sense to me. Please check clock frequency deviation of ADXL362, on page 12 of ADXL362 datasheet, figure 29. You can find that the ADXL362 internal clock frequency deviation can over 10% although most parts are <= 10%. For some parts, the deviation can reach +/-16%, then the error (-10.75%) you see is make sense. ADXL362 support external clock and external trigger signal, if the accuracy of the clock frquency is important to your application, you can consider to use the external clock or external trigger signa.
Hope these can help.
BR
Neil