A few questions @Sqaut
I assume you used the manual walk mode on your tracker?
Was the tracker connected to your phone, and you had your phone with you?
If so did you get a map of your walk displayed?
Was the walk inside where GPS will not work and you turned off GPS or did not have the offline with you?
Without GPS the Charge 2 will count your steps ans multiply then by the stride.
If your not using the GPS we need to determine if the step count is correct since the Charge 2 will not be able to measure the distance.
You say that you walked 6 K but the tracker says 1.5 miles, why is the tracker not measuring distance in kilometers?