Is this item and its links being created by software you have written? If so, can you say a bit more about how it works and perhaps provide the code for review? If you do the same work item and links creating using an RTC client, does it work correctly?

Hi Millard,
Yes it is created by code I have written, both the workitem and the links. Actually the workitem is created successfully no matter the automatic links code exist. If I add the automatic links code the issue appear. But in the workitem view, I am sure the links are created successfully because they are in the Tab Links view, it just can not be clicked. Here is my code for creating links:
    source = IReferenceFactory.INSTANCE.createReferenceFromURI(new URI(url));
    IReference target = refFactory.createReferenceToItem(taskWorkItem);
    ILinkService linkService = getService(ILinkService.class);
    ILinkServiceLibrary linkServiceLibrary = (ILinkServiceLibrary) linkService.getServiceLibrary(ILinkServiceLibrary.class);
    ILink link = linkServiceLibrary.createLink(WPMConstants.LINK_TYPE_OUTPUT, source, target);
    linkServiceLibrary.saveLink(link);
          

PS：  This part works well on RTC 3.0.1.2, now we upgrade to RTC 4.0.2, the issue appear

I focused on a Task workitem which had parent, found the code location in firebug:
if(arguments.length==3&&!_10._validateRequestParams(_f)){

}
Snapshot for parameter _f :
 

In targetLinkItemIds.  'undefined' is the problem. _edExxx is the parent's Id. And the xxxoutputlink type is created programmatically.  But I didn't find any method to set the undefined id to a real UUID in Link code, there just two set method exist.
    link.setContextId(UUID.generate());
    link.setRequestedStateId(UUID.generate());