This issue has now been FIXED, please update the Endomondo App on the watch to version 1.1.2.
We are currently experiencing some issues registering distances for workouts which are tracked via the Endomondo app for Samsung Gear Fit2, S2 and S3 smartwatches. Our team is aware of this issue and is working together with Samsung on solving it as soon as possible.
In the meantime, please track your workouts via the Endomondo phone app in order to register your distance correctly.
Thank you very much for your support and please accept our apologies for any inconvenience caused.