The machines have made the biggest difference for US arrival.

I remember stepping off BA215 in 2014 when half a dozen other European jets were still being processed at customs, including the earlier BA flight! Almost 3 hours later........ we emerged (with the final BA flight at the back of our queue).

The next time I landed, the machines were in place which massively increased the processing capacity. Through in 10 minutes?

I think flights which land at very busy times (like both BA's LAX flights) are going to be more susceptible to horrendous queues...