OR condition doesnt work properly in JPA Query

Question

i have the following entities

class ProductUnitOfMessure
@ManyToOne
@JoinColumn(name="PRODUCT_ID")
private Product product;

@ManyToOne
@JoinColumn(name="VARIANT_ID")
private Variant variant;

---

class Product
@OneToMany(mappedBy = "product", fetch = FetchType.LAZY)
List<Variant> variants;

---

class Variant
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "PRODUCT_ID")
private Product product;

Now when i run the query

select p from ProductUnitOfMeasures p where p.variant.sku=?1 or p.product.sku =?1 (sku of type String).

it return empty list, although there are some as per the below ProductUnitOfMessure table ProductUnitOfMeasures

when i only run select p from ProductUnitOfMeasures p where p.product.sku =?1 i get some values, why this is happening even though i use OR not AND ?

database is oracle