The complex option is not available when using mass update in administrator mode. There is a bug in the db.environment RAD on the set.admin.env.2 panel. Work around by creating an alias for the complex.update field in the docenv dbdict. The alias name should be db.complex.update.
The se.search.engine sets up an environment variable using the db.environment RAD. The environment structure is based on the docenv dbdict. If the dbdict has an object and admin mode is NOT selected then the environment app in the object is used to build the environment variable. Access to mass update depends on the configuration of the list state.
If the dbdict does not have an object then the db.environment RAD is used to build the environment variable. The environment variable structure is based on the docenv dbdict. Contents of the environment variable are based largely on the privileges in the master FC.
When administrator mode is checked then the db.environment forces the values to true. However, there is a discrepancy between the field name for complex update access in the RAD and the docenv dbdict. On the set.admin.env.2 panel the expression sets db.complex.update in $L.env=true and complex in $L.env=true. But the fields in the docenv are db.complex and complex.update. An easy fix is to create an alias for complex.update in docenv called db.complex.update. This will cause the complex option to appear in admin mode.