question

You might need to give some more details before someone can fully answer your question, but it looks like the issue is with the timing of when a Sink closes its input ports versus when the destination of the boxes on the Racks are determined.

For example, it's possible that more than one Transporter will be in transport to a given Sink at one time. So one Transporter might deliver a box to the Sink and the message is sent to one of the nearby Queues to create a number of flowitems in that Queue. And when the condition is met, that Queue will close the Sink's input ports.

However, it's possible a second Transporter could already be on its way to the same Sink when the first Transporter drops off its box. That means the second Transporter will still deliver its box to the Sink even if the Sink's input ports are closed during that delivery time.

In fact, if one of the upstream Racks has already fired its Send To Port logic and picked that Sink before the Sink's input ports are closed, a Transporter will still come pick up the box and deliver it to the Sink even if the input ports are closed during the process. Closing the input ports on the Sink will only affect new boxes that are trying to leave a Rack when they cause the Rack's Send To Port logic to fire.

I'm not too sure what you should do to fix the issue. The tricky thing is trying to control an upstream object using transports with a downstream object's OnEntry trigger. If you executed the logic that is currently in the Queue's OnEntry trigger earlier in the process, but don't create the flowitems in the Queue until the box reaches the Sink, that would give you more control.

You would have to do it after a box's destination Sink is determined on a Rack, but before a transport is requested. So you could use dummy Queues between the Racks and Sinks to perform the necessary logic in their OnEntry triggers and more the "Use Transport" logic from the Racks to the dummy Queues.

You could also try using Process Flow and Lists to handle the logic as well as the transportation. You would need to rework the model a little bit, but I don't think it will take too much effort.