TL;DR
When dealing with multiple storage chests at the same priority level, use the closest one with space in it instead of using the last one to have its inventory updated when choosing where to drop off materials.

What?

Consider when you have a large base with a number of yellow storage chests ...

Whenever the contents of the chest change it's moved to the front of the list of 'chests with this item in it'.


Ah well that would explain what I'm seeing then. Is that the way it should work though? It can lead to some pretty unintuitive behaviour.

What's the reason behind it not using the ...

What qualifies as the "first" chest though? I can tell you it's not the first chest I placed that the bots are using, and note that the bots in the example I've provided don't drop into any single chest but instead seem to spread their dropoffs between any chests that have had items inserted ...

Sorry but no, every relevant chest already has copper wire in it. You can see that in the save.

I have attached a save which led me to this discovery.

In the save you will spawn near a decider combinator with an extra blank condition. If you remove that condition the copper wire production next to it will begin.
03-16-2026, 22-20-30.png

You will notice that the bots pick up copper plates ...