We went live recently and since that moment, we are having problem with this DataSource. We've been able to complete the Init and the Delta ran 1 time (the day after). Since then, it's scheduled to run every night but the data package are always empty.
2LIS-11-VASCL and 2LIS-11-VAITM are running in Full and are executing with success every night which gives us the idea to turn 2LIS-11-VAHDR in Full too. We are not very concerned by the volume of transactions in Sales Order. That's not what triggered the Init/Delta choice.
I'm now looking for the steps to follow to turn VAHDR in Full. I know that I have to adjust the Process Chain too. Any recommendations are welcome too. Here's a snapshot of the PC: 
Thank you all for your help!