Item substitution not working for B2B items

Summary:

Item substitution not working as expected for Back to back items having Buy or Make flag enabled

Content (please ensure you mask any confidential information):

Items are back to back enabled(either Buy or Make flag as Y). Some items have substitute relationship set at master org level with planning enabled set as Y. ATP rules and sourcing rules are setup. When the sales order is created with B2B Buy item having no onhand, ideally GOP should substitute the item if substitute item has onhand. However, we observe below behavior though onhand of both the items is collected and review supply availability shows correct onhand status.