Hello
It is possible that somehow the CALL TRANSACTION checks changed for CJ20N? (Transaction SE97 to maintain settings). There you can configure that, when a program/transaction calls a different transaction (so CJ20N calling CJI3), if SAP executes a check on S_TCODE..So in case this is active for CJ20N, then the users need to have access to CJI3 also. By changing the check indicators is SE97 you can change this behavior.
I checked in one of our development SAP systems (ECC 6.0) and in our system the check from CJ20N to CJI3 is not active.
SAP Note 358122 describes the functionality of SE97.