> The data load fails due to "ORA-01427: single-row subquery returns more than one row tips". But this same query works with Result cache but fails with this error when IMV is enabled.
You'll need to produce query plans both ways. In theory the only difference for the materialized view load will be that the user criteria here won't be used initially as all data is needed to populate the materialization table.
> Is there any config settings that needs to be changed?
No, that is never expected. You may be hitting a known issue that is addressed by a later patch level. You'll want to contact GSS with your stacktrace.