I have a oneplus two.
When hoppers are placed one over another and rail is placed above them upon which a minecart with chest is placed and the first hopper is connected to a comparator the comparator does not get activated when the first hopper takes the object from the minecart with chest but gets activated if manually objects are put into the hopper
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What is happening is that the item is not in the hopper long enough for the comparator to work. When hoppers are placed like that the top hopper sucks the item out of the chest and then the bottom hopper sucks the item out of that hopper all in one tick/update. When you place the item in the hopper the item is in the hopper for at least 1 tick before being pushed/sucked into the next one allowing the comparator to see that.
What is happening is that the item is not in the hopper long enough for the comparator to work. When hoppers are placed like that the top hopper sucks the item out of the chest and then the bottom hopper sucks the item out of that hopper all in one tick/update. When you place the item in the hopper the item is in the hopper for at least 1 tick before being pushed/sucked into the next one allowing the comparator to see that.