Usually, when we filter the type as inbound shipment, nothing will be shown under the related records subtab of item record even if there is an inbound shipment existing. The following is a solution to this.
Create Inbound Shipment saved search as follows:
a. Lists > Search > Saved Search > New > click Inbound Shipment
b. Add Search Title
c. Leave the Criteria tab blank
d. On the Results tab > show the fields you wanted to see on the result
e. On the Available Filters > add the filter ‘Item fields… : Internal ID (Number)
f. Save and Run
2. Create a custom sublist
a. Customization > Forms > Sublists
b. On Custom sublists page > go to Item and set the following:
*Search = Select the saved inbound shipment search created above
*Label = add desired Label for the custom sublist (e.g. Inbound Shipment)
*Tab = select from the dropdown
*Inventory = check this box to show the custom sublist on all inventory item records
c. Save
Go back to an item record > go to the tab you selected > you should now be able to see the custom sublist for the inbound shipment.