Hello!

Loaders tend to use one line over another when backlogged and fill only single line when under-loaded. Will try to provide some kind of evidence savefile later.

Thanks.

This is normal. Inserters prefer one side of a belt when pulling from the belt, and if usage is slow enough that only one inserter is required, you will see the behavior described. Changing it would require changes to Factorio core logic.

What about instances where it would use both inserters, though? I've had instances where multiple full belts are going into a cargo wagon or warehouse (love that mod, btw), but only one side is being used despite there being enough of a load to require all inserters.

I’ve not seen this happen except in the case of using another mod that increases belt speed but doesn’t properly handle miniloaders.

If you have a save that demonstrates this problem I can have a look at it.