MPU6050 sampling rate bug


I am trying to get a measure from the MPU6050 accelerometer every 20 ms but every 800 ms there is a bug and it takes the next measure only 200ms after. My code doesn't do anything special every 800ms so I don't get why it happens...

I am logging the data from the accelerometer in an SD card. Can it come from a bad connection with the SD card module? I am also taking measurement from a GPS every 30 seconds. Can it cause the problem?

I am using an arduino uno.

Thanks for your answers!