Hello, I faced the same problem. I did see the required privilege already assigned to _SYS_REPO from the GUI. To make it work, I re-executed the grant SQL. Magically, it started working.
grant select on schema <Schema_Name> to _SYS_REPO with grant option;
An option that I could have probably considered troubleshooting this would have been to run a SQL and check what privileges does _SYS_REPO have on my desired schema.
select * from sys.granted_privileges where grantee = '_SYS_REPO' and schema_name = <Schema_Name>;
Thanks,
Prabhu DC