MPU9250 and MPU6050 not working with SAMD21 board

Question

I am trying to use an MPU6050 with my SAMD21-based board (a LightAPRS W-2), but it doesn't work.

The sensor definitely works, as I can get data from another 3.3 Vlogic-level board, and the sensor works with a level shifter with an Arduino Uno.

I do not know what is wrong. My SAMD21 board I2C works fine with other devices, but both the MPU6050 and the MPU9250 don't work. Here is the code I use:

/***************************************************************************
* Example sketch for the MPU9250_WE library
*
* This sketch shows how to measure pitch and roll angles from the MPU9250. 
* I have also included the corrected angle method for comparison.  
* 
* For further information visit my blog:
*
* https://wolles-elektronikkiste.de/mpu9250-9-achsen-sensormodul-teil-1  (German)
* https://wolles-elektronikkiste.de/en/mpu9250-9-axis-sensor-module-part-1  (English)
* 
***************************************************************************/
#include <MPU9250_WE.h>
#include <Wire.h>
#define MPU9250_ADDR 0x68
/* There are several ways to create your MPU9250 object:

MPU9250_WE myMPU9250 = MPU9250_WE()              -> uses Wire / I2C Address = 0x68
MPU9250_WE myMPU9250 = MPU9250_WE(MPU9250_ADDR)  -> uses Wire / MPU9250_ADDR
MPU9250_WE myMPU9250 = MPU9250_WE(&wire2)        -> uses the TwoWire object wire2 / MPU9250_ADDR
MPU9250_WE myMPU9250 = MPU9250_WE(&wire2, MPU9250_ADDR) -> all together
Successfully tested with two I2C busses on an ESP32

*/
MPU9250_WE myMPU9250 = MPU9250_WE(MPU9250_ADDR);
void setup() {
  Serial.begin(115200);
  Wire.begin();
  if (!myMPU9250.init()) {
    Serial.println("MPU9250 does not respond");
  } else {
    Serial.println("MPU9250 is connected");
  }
/* The slope of the curve of acceleration vs measured values fits quite well to the theoretical

values, e.g. 16384 units/g in the +/- 2g range. But the starting point, if you position the
MPU9250 flat, is not necessarily 0g/0g/1g for x/y/z. The autoOffset function measures offset
values. It assumes your MPU9250 is positioned flat with its x,y-plane. The more you deviate
from this, the less accurate will be your results.
The function also measures the offset of the gyroscope data. The gyroscope offset does not
depend on the positioning.
This function needs to be called at the beginning since it can overwrite your settings!

*/
  Serial.println("Position you MPU9250 flat and don't move it - calibrating...");
  delay(1000);
  myMPU9250.autoOffsets();
  Serial.println("Done!");
/*  This is a more accurate method for calibration. You have to determine the minimum and maximum

raw acceleration values of the axes determined in the range +/- 2 g.
You call the function as follows: setAccOffsets(xMin,xMax,yMin,yMax,zMin,zMax);
Use either autoOffset or setAccOffsets, not both.

*/
  //myMPU9250.setAccOffsets(-14240.0, 18220.0, -17280.0, 15590.0, -20930.0, 12080.0);
/*  Sample rate divider divides the output rate of the gyroscope and accelerometer.

Sample rate = Internal sample rate / (1 + divider)
It can only be applied if the corresponding DLPF is enabled and 0<DLPF<7!
Divider is a number 0...255

*/
  myMPU9250.setSampleRateDivider(5);
/*  MPU9250_ACC_RANGE_2G      2 g    (default)

MPU9250_ACC_RANGE_4G      4 g
MPU9250_ACC_RANGE_8G      8 g
MPU9250_ACC_RANGE_16G    16 g

*/
  myMPU9250.setAccRange(MPU9250_ACC_RANGE_2G);
/*  Enable/disable the digital low pass filter for the accelerometer

If disabled the bandwidth is 1.13 kHz, delay is 0.75 ms, output rate is 4 kHz

*/
  myMPU9250.enableAccDLPF(true);
/*  Digital low pass filter (DLPF) for the accelerometer, if enabled

MPU9250_DPLF_0, MPU9250_DPLF_2, ...... MPU9250_DPLF_7
DLPF     Bandwidth [Hz]      Delay [ms]    Output rate [kHz]
0           460               1.94           1


1           184               5.80           1


2            92               7.80           1


3            41              11.80           1


4            20              19.80           1


5            10              35.70           1


6             5              66.96           1


7           460               1.94           1



*/
  myMPU9250.setAccDLPF(MPU9250_DLPF_6);

}
void loop() {
  xyzFloat angles = myMPU9250.getAngles();
/* This method provides quite precise values for x/y 
   angles up 60°. */
  Serial.print("Angle x = ");
  Serial.print(angles.x);
  Serial.print("  |  Angle y = ");
  Serial.print(angles.y);
  Serial.print("  |  Angle z = ");
  Serial.println(angles.z);
/* Pitch and roll consider all axes for calculation. According to my experience
   it provides more reliable results at higher angles (>60°) */
  float pitch = myMPU9250.getPitch();
  float roll  = myMPU9250.getRoll();
Serial.print("Pitch   = "); 
  Serial.print(pitch); 
  Serial.print("  |  Roll    = "); 
  Serial.println(roll); 
  Serial.println();
delay(1000);
}