I have commented a few times upthread about this, but my guess is that in about three quarters of cases where people constantly have problems it's due to technique (pressing down passport correctly), followed by significant changes to face compared to photo in the passport. Beards, spectacles, hats. If you don't then clearly stare at the camera lens, ideally using a similar expression as used on the passport, then it's not surprising if you get rejected thanks to a blurred view of the side of your face.There is a knack to it, but you can see upthread that those FTers who go through the UK Border every week are not, on the whole, participants in this thread.