CBO not choosing indexnl join when there are multiple join predicates

CBO does not pick an indexnl join when there is more than one join predicate.
The following query results in a hash join plan even though there is a valid indexnl hint on one of the predicates.

select * from R join S on tobigint(R.u64) = S.u64 and tobigint(R.u256) /*+ indexnl(S_u256_idx) */ = S.u256 where R.rand < 10;