question

That's because the PassTo of the dispatcher is not looking for already allocated work.

Use this code for the PassTo which has a section to look for a matching destination of any AGV:

treenode tasksequence = param(1);
Object current = ownerobject(c);
/**Pass to the object closest to the destination if available*/
/**If the object is on a network, then network travel is calculated; otherwise centroid-to-centroid distance is used.
/**Consider available objects only if none are found, then the tasksequence will be queued up using the
Queue Strategy, and will be sent to the first available.*/
double curmin = GLOBAL_UNREACHABLE;
int minindex = 0;
treenode destination = NULL;
for (int taskrank = 1; taskrank <= gettotalnroftasks(tasksequence) && destination == NULL; taskrank++) {  // this finds the first task in the tasksequence that is a travel task.
    if (gettasktype(tasksequence,taskrank) == TASKTYPE_TRAVEL)
        destination = gettaskinvolved(tasksequence,taskrank,1);
}
if (destination==NULL) // first available if there is no travel task
    return 0;

//Check if there's a matching destination.
for (int index = 1; index <= current.outObjects.length; index++) {
    treenode curobj = current.outObjects[index];
    if (curobj && isclasstype(curobj, CLASSTYPE_TASKEXECUTER)) {
        if (inputopen(curobj)){
            treenode  ts=gettasksequence(curobj,0);    //TaskSequence  ts=gettasksequence(curobj,0);  
            if (objectexists(ts)) {
                int curtask=getcurtask(ts);  
                for (int taskrank = curtask; taskrank <= gettotalnroftasks(tasksequence) ; taskrank++) {  // this finds the first task in the tasksequence that is a travel task.
                    if (gettasktype(tasksequence,taskrank) == TASKTYPE_TRAVEL) {
                        Object taskdest = gettaskinvolved(tasksequence,taskrank,1);
                        if (taskdest==destination)
                            return index;
                    }
                }
            }
        }
    }
}

for (int index = 1; index <= current.outObjects.length; index++) {
    treenode curobj = current.outObjects[index];
    if (curobj && isclasstype(curobj, CLASSTYPE_TASKEXECUTER)) {
        if (ipopen(curobj, opipno(current, index)) && inputopen(curobj)){
            double curdist = distancetotravel(curobj, destination);
            if (curdist != GLOBAL_UNREACHABLE && (curmin == GLOBAL_UNREACHABLE || curmin > curdist)) {
                curmin = curdist;
                minindex = index;
            }
        }
    }
}

return minindex;