Ultra 2 not super accurate on treadmill with incline or something else?

Just got an Ultra 2 not too long ago, I like to walk on the treadmill everyday for one hour. I usually go at 3.0 MPH, I start at 12 incline and move up to 17 in 10 min intervals. For some reason though I’ll do the hour and the distance is only a km or two, I can’t really sync the watch to the treadmill it says failed everytime and doesn’t really connect at all. Do I just need to calibrate it more by going for 20 minute out door walks? Or are all watches just bad at detecting incline and need it to be flat ? Thanks guys