Somehow small storage is pumping out more than it can accept from an input sources
Stable release

Somehow small storage is pumping out more than it can accept from an input sources
Stable release

Could you add two more outputs after the large storage unit, using the same pipes and consumption rates, and see what happens? Or have you already done that?
The small storgae has a maximum throughput of 900.
If I remember correctly, it is input that is throttled, not output, so it will run the full belt out until the storage is empty, but inputs will be restricted to the states limit. (I know it was this way in the past - it may have been changed since).