Accel calibration incorrect with mpu_real

[Bestagon]

When running mpu_real with ESP32 and MPU6050, the pitch drifts from 0 (correct - in upright position) to 6 degrees in about half a second after starting, then the value stabalizes. Similar problem with Roll. When I delete the fusion with the pitchAccel like this:

//pitch = gyroPitch * 0.95f + accelPitch * 0.05f;
pitch = gyroPitch;

The pitch value is correct. But i want the fusion to work...

I checked the acceleration offset values for x,y and z and changed them manually until
accelG.x = 0, accelG.y = 0 and accelG.z = 1. Now the pitch / roll values are correct when using the fusion with accelPitch and accelRoll. The gyro calibration seems to work fine.

Any idea why the acceleration calibration gives wrong offsets?