There are a few requirements a product must fulfill to be listed as a product with low stock.
Product type needs to be set to simple or variation (variation of variable product type). Variable, grouped, and external type is not listed.
It needs to have the setting “stock management” enabled.
The setting “Low stock threshold” (located in the “In Order & Inventory Manager” tab, not in “Inventory”) needs to have a lower value than the current stock.
It needs to have the setting “Enable warning for low stock” checked. This option is located in the “Order & Inventory Manager” or “Variations”-tab on the product edit page.
The meta “Meta: oimwc_supplier_show_in_low_stock” have to be set to “yes”. This is only accessible when importing product data.