Domestic from LHR - Gate 11:
3 lanes, Gp1, 2&3, 4&5.
1 and 2 called at the same time which meant that due to the narrow lane in 1, and 2/3 too, meant the these groups really boarded together.
Unfortunately for the Gp1 lane the self scanner was playing up with most of the G1 BP's which meant 'switching over' to the G2/3 scanner which was the only other one at the gate. Flight was about 1/2 to 2/3rds full. There were only about 10 passengers in the G1 queue so why not just let them board first then move onto the 2nd lane for G2 and 3? After the tech issue one of the GA's started just manually boarding.