In SAP HANA system _SYS_REPO user is required to create run time objects that are saved in HANA database under _SYS_BIC schema. When you activate modeling views in HANA, SYS REPO provides the read access to users on these modeling views. That is why it is required to grant _SYS_REPO with SELECT with GRANT privilege to user schemas.
GRANT SELECT ON SCHEMA "SCHEMA_NAME" TO _SYS_REPO WITH GRANT OPTION
This is required when you use objects of a table/view of a schema to build HANA Modeling Views. You need to grant _SYS_REPO the SELECT WITH GRANT privilege on this schema.