Ok, check 2 things.

1. Request on behalf of is a field on RITM table and not on request or task table.

2. Look for a table level ACL on RITM which gives access to opened for or requested for user access to view the RITM. If the ACLs are restricting then his filter will not work.

Also you can check if the request on behalf of user can view the RITMs at backend.