How to Change the Output Data Rate (I2C) of ADXL355 with Ardunio MKR

I'm using between 1-4 ADXL355 tri-axial accelerometers (https://www.analog.com/media/en/technical-documentation/data-sheets/adxl354_355.pdf) in conjunction with an Arduino MKR WIFI1010 in a test setup. Ideally I would like to sample close to 500 Hz with each whether that is testing with 1 sensor or with 4 using the TCA9548A I2C Multiplexer. Currently, I am collecting around 200 Hz with 1 sensor or 50 Hz with all 4 sensors (different code used for this setup). The default for the ADXL355 is 500 Hz, which makes it even more strange I cannot sample at that rate.

I have tried to increase my baud rate from 9600 to 128000. I have tried to use Wire.setClock() to maximize the I2C speed to the maximum of 3.4MHz which the sensors and the Arduino can operate at. I tried to save to a micro SD using a shield at one point too, though most of my testing has been with the Serial Monitor. I altered the Wire.write() which should be what is controlling the output rate, however even when I set it to the 4kHz setting (Wire.write(0x00)), I still am sampling at ~200Hz.

#include <Wire.h>
#define ADXL 0x1D                                       //Datasheet pages 4 and 7 have info that will be necessary for future development. 

void setup() {
  Wire.begin();                                         // initiate the accelerometer   
  Wire.setClock(3400000L);
  Serial.begin(128000);                                   // initiate the serial monitor  
  delay(100);   
  Wire.beginTransmission(ADXL);                         //set STBY bit 0 to low / turn on MEASURE mode 
  Wire.write(0x2D);   
  Wire.write(0x00);   
  Wire.endTransmission();  
  delay(100); 
  Wire.beginTransmission(ADXL);                         //set RANGE to +/- 2g  pg. 37 of data sheet
  Wire.write(0x2C);   
  Wire.write(0x01);   
  Wire.endTransmission(); 
  delay(100);
  Wire.beginTransmission(ADXL);                         //set data rate to 4000HZ page 37 
  Wire.write(0x28);
  Wire.write(0x00);
  Wire.endTransmission();
  delay(100);
}

I am expecting to get 500Hz (or 4000Hz how my code is right now) but am getting the 200Hz, and altering the set data rate does not seem to influence the results. Any help increasing my sample data rate would be appreciated! Thanks!