Not exactly certain, but seems 777146 was undergoing some form of testing before being dragged out yesterday after the disaster start of service. Assuming it was being used for testing of new systems, as we now have better HBL announcements, and a male announcer in combination with Julie.
With the shoes, one can assume they were frozen over as theres been constant issues with them and switching between 3rd rail and battery.
Wouldn't reckon they were introduced too fast, but just that there should have been a provision to serve Kirkby with 507s/777-0s in the interim while they get up to a constant 2tph without any issues.
Though its commonly known by locals that Rotherham forced the rollout, so, perhaps.