I wanted to make an item sorter for my iron golem farm. Flowers would go to the right - they would be put into a composter, and iron ingots would go to the left.
I used this type of item sorter.

If you didn't know, hoppers prefer going to the bottom and then going to the sides.

So I thought that it can be caused by chunks, as it is in this case. But no.
Rather than going to the bottom, the hopper is going to the sides and dividing them to 2 chests. It's really weird and complicated.

Here are my observatios:
If a hopper is an input, then items from that hopper divide like this

If a chest is an input, items go to the chests as they should.

• they firstly go to chest A1, then hopper B1, and if they are full, then items go to chest A2 and lastly to hopper B2.

However, if a hopper is an input and there is more than 2 chests, then items go like this.

Also if chest A1 is full, yet chest A3 isn't, items will start to pile up in hopper B1, untill chest A3 and hopper B3 aren't full. If they are, then they will start to go to chest A2, then B2 and lastly they will stay in hopper B1.

It seems that the input hopper throws out items way faster than ither hoppers cans.

This weird behaviour doesn't seem to occur when input hopper is placed sideways.

I hope you have a nice day.