When you update the password of a user (i.e. the password was already prodyctive) it is set to initial rather than productive. users have to change their password at first logon after reset.
ABAP security controls mean that the IdM communication user must logon with SNC in order that the password is set to productive status.
Enable SNC between the IdM Application and the ABAP Server. This is detailed in the appendix of the guide Identity Management for SAP System Landscapes: Configuration found in the IdM 7.2 documentation centre
Ensure that in the UpdateABAPUser pass that the ProductivePWD attribute is set to X
In the ABAP server ensure that the SNC name of the IdM communication user is maintained in its' SU01 account. See note 1901008 for more detail
For setting a productive password in other scenarios on ABAP servers see note 1575445 - Setting productive password in ABAP Systems