I have been playing with the X-T2 and found that it doesn't seem to like AF tracking at the extreme end of the 18-135mm 'Super Kit' lens...
It focuses once but does not re-focus as the subject/camera distance shifts.
If I zoom back to around 100mm then I have no issues... I have updated the lens to the latest firmware.
I posted this on the DPReview Forum and other posters have reported the same issue when they tried it…
Chris