When an item exits the Intermediate Stock queue (IS) while its content is less than 40 and there are at least 10 items in the Raw Material queue (RM), a message is send which then causes 10 items to be released from RM. This can happen multiple times before the initially released items have actually been picked up at RM. The same items are then released again which also causes a second transport task sequence to be created for those items.
When this second task sequence is executed the transporter will first travel to the network node at RM, since that is stored as the original pickup location in the sequence. But because the items have already been moved, the transporter will then offset travel to the actual item location in IS. The offset travel happens in a straight line. After loading the items the transporter will return to the RM network node and then travel to the network node at IS and unload the items.
So what you need to do is to make sure that the items are not released twice. You could do this by setting a label on IS that prevents further messages from being send until the ordered batch has arrived in the queue. Or you open/close the output of RM instead of holding and manually releasing the items (close the output every ten times the Send to Port code has been executed - which is synonymous with an item having been released. And open it with the same message that is currently causing the release).
