missing volume ICM

Hello,

I have following situation in my model: a storage node with incoming flow from a weir and outgoing flow through a pump.
The problem is that the volume of incoming and outgoing links do not match. The storage has no lost volume and the peak volume for this node is 6m3.
Volume balance (m3) is -2.834 and Volume balance (%) is 0.019 for the storage if this is any help for you. The storage is not flooding.
Attachment 485

So where is the missing volume? Any thoughts will be appreciated.

Thanks!