Distance for drone starts count not from first portal, but from the place, where you sent drone from agent
Try to check that distance
If problem still exist, please, write extended description of your problem
Drone Launch Location: 53.165647, 8.944990
Distance from Launch to final portal: 13,77 km - so even more.
I was traveling from North to South.
Im not sure what should explain further, the distance between point a and b is 13,45 (13,77) km and the game says its 11 km. I dont know what i could do to be more precise in my description of the issue.
@Alisizer is incorrect. Travel distance is from the first portal your drone goes to when you launch it, not where you are standing when you send it there. I have tested this by observation (start portal was over 1km from my actual position, distances were always consistent with the first portal, not where I was standing) and I am pretty sure it is stated somewhere by Niantic staff, probably Brian Rose.
The distance is not rounded but any digits after the decimal point are truncated - so if launch is 13.77km away and start portal is 13.45km you should expect to see the same result of 13km.
I thought perhaps you had run into issues with the way the distance is calculated as there are several ways to calculate distance around the earth, and many values used for the earth's radius - but over such a short distance you would not see a difference of 2km.
My calculations also give a value of approx 13.45km from that start and end portal - and when I have tracked my drone flights it has been very accurate - distance in app has changed/not changed as calculated to cm of accuracy.
Have you tried restarting the app and checking again? I often find that if I look at my stats some of my drone jumps have not registered in my stats, but a restart fixes that.
Are you absolutely certain that https://intel.ingress.com/?pll=53.16374,8.941443 was the very first portal your drone went to after it was last returned to you?
If the distance has still not registered and you are 100% certain the drone started on the first portal you mentioned and travelled to the 2nd, then yes - it sounds to me like there is a bug in your distance somehow.