The 'Related to workflow' is blank after sync search database. why?

I had set up the search database and sync search database. But after I sync the
search database, and I open the forms, all the forms has "Related to workflow"
tab but in some of the forms, the "Related to workflow" is blank although there is
active links running on that particular field.

First, check if your AR Server licensed?
If your AR Server is licensed, there is another possibility :
If you or another administrator exits Remedy Administrator while the database is being synchronized, you will
not be able to perform an object search because the system assumes that the database is still being
synchronized. To correct this problem, perform one of the following tasks:
A. Delete the three search forms: object_search_admin, object_search_details, and object_search_ref. Then, set
up the database again.
B.Open the object_search_admin form in Remedy User. Perform a search and modify the first request by
entering 0 in the Run/Not Run field. When the synchronization is running, the Run/Not Run field contains a 1.
When you enter 0, the system knows that synchronization is not running.