If you look really closely on the inside panel of the gate dividers, you'll see some little red dots. These are part of a presence detector. If you trip one of these the gate stops responding. So, say you are traveling with a child and you have them ahead of you as you try to check them through the gate. They trip the sensor and the gate doesnt work. The same often happens when people put their suitcase in front of them. I often find passengers stuck trying to get through the gate like this
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