Item Rules set function ConvertToUOM is not functioning as expected in Validation rule set

Summary:
We have a requirement to create a validation rule set with the following criteria:

1. The Physical Unit weight and its Unit of Measure (UOM) must match the Environment Levy Weight and its UOM (EFF Attribute).
2. If the UOMs differ, the rule should validate the converted value using UOM conversion.

To meet the requirement in point 2, we used the ConvertToUOM function. However, it fails to convert values to Kilogram, the target UOM when there's a mismatch between the Physical Weight and Environment Levy Weight UOMs.

Validation Condition : [Item].[Physical Attributes].[Unit Weight] == [Item].[Environmental Levy Material (IMO)].[Weight] and [Item].[Physical Attributes].[Weight Unit of Measure] == [Item].[Environmental Levy Material (IMO)].[Weight UOM] or [Item].[Physical Attributes].[Weight Unit of Measure] != [Item].[Environmental Levy Material (IMO)].[Weight UOM] and ConvertToUOM([Item].[Physical Attributes].[Unit Weight]; "Kilogram") == ConvertToUOM([Item].[Environmental Levy Material (IMO)].[Weight]; "Kilogram")