question

The key to making your model work they way you want in understanding what happens when multiple tokens are all waiting for the same event. At time 912.5 right as the first flowitem arrives at DP2 there are 20 flowitems all waiting for DP2's OnArrival event. By default, this means once all the tokens hear the event happen they are all released to the Acquire activity, even though the flowitems those tokens represent aren't actually at DP2. So once the first token releases the elevator, the next token immediately acquires the elevator even though the item is way upstream of the elevator.

Luckily there is a simple fix. Under the Wait for Event;s properties you will see this table:

This shows data that is available from the event you are listening to. Make it look like this instead:

This means that in order for a token to be released from the activity, the token's 'item' label has to match the flowitem that actually caused the OnArrival event. So only one token gets released to your acquire, instead of all the waiting tokens.

On an unrelated note, you don't need your "Send item" picklist option on DP2, since your process flow is doing the loading and unloading, and since it's throwing an Array index out of bounds exception, I'd remove it.