Thing happens:
If you put multiple items in one slot in the crafter, the comparator circuit will only confirm that 1 item appears in the crafter.
Steps to reproduce:
1. Place the crafter and behind it place the comparator and the redstone that leads away
2. Place an item in any box in crafte
4. Place multiple items in any box in crafter
5. You will find that the strength of redstone is equivalent
This is working as intended. From the changelog "The Comparator signal strength is 0-9, where each non-empty or toggled slot adds 1 strength"
Increasing the number of items in a slot does not increase strength. Strength is increased by how many slots are being used. The unofficial wiki helps to explain this https://minecraft.wiki/w/Crafter#Redstone_component
"The signal strength is equal to the number of crafting slots that are either disabled or occupied by an item. The stack size of the item has no effect on the comparators output signal e.g. having 1 stick in a slot vs having 64 sticks in that same slot both output the same comparator signal."
(Please note the wiki is not an official source of how things should work, I have attached it solely for a further explanation for you)