In the movie there are only two times where we see a computerized system fail, both occur at the same machine with the same task. This implies a level of sophistication in the worlds software and hardware technology because we only see a computerized system fail twice throughout the entire movie. The problem that is seen happens to the technology in our world as well meaning that the technology still has areas for improvement.
When we do see a failure it is when our main character #325 and #325's friend try to get a green apple from a vending machine. Both times the item is finally dispensed after a character reaches up the item dispenser door in order to move a latch to dispense the stuck item [1]. The type of vending machine seen uses a spiral rack in order to dispense items, this type of vending machine exists in our world and items that this type of rack has a higher than normal chance of the item getting stuck if the spiral is not pointing upwards [2]. Which when the vending machine fails, the screen that acts as a window into the internal state of the vending machine shows the spiral as facing to the left not in the ideal position [3]. Despite this the rest of the technology that pertains to the vending machines works flawlessly, we never see any device fail at interpreting a gesture or associating a purchase to the wrong user. Meaning that the software involved is developed to near perfection.
[1] Black Mirror: Fiftenteen Million Merits (5:32 & 17:32)
[2] Cao, Y.; Ikenoya, Y.; Kawaguchi, T.; Hashimoto, S.; Morino, T. A Real-Time Application for the Analysis of Multi-Purpose Vending Machines with Machine Learning. Sensors 2023, 23, 1935. https://doi.org/10.3390/s23041935
[3] Black Mirror: Fiftenteen Million Merits (17:30)