Originally Posted by corporate-wage-slave

This sounds like one of the newer Brexit passports, with the super hard data page. The main cause of failure with these are sliding on the glass, because it's so slippery a surface, followed by allowing some daylight to come in from the sides which then blanks out the scan via reflection. It's the opposite to the last series of EU passports which had a very flimsy data page, for which the hair clamp would work. If the Border Force agent said there wasn't anything wrong with your passport then it's likely to be technique, either over firmness with the push down (thus causing the first issue) or insufficient pressure (causing the second). If this is just after 2 uses I would give it a little longer before declaring it a dud.