You can't do that in beforeLoad. You need to do it in preferably in afterSubmit so you know the Item Fulfillment saved correctly.

Thanks @creece Before Submit and After Submit events are not triggered if inventory details are not available.

I'd check your deployment as that is not true.

This is script record

Are you the owner? its in testing mode currently

yes I am owner

You'd have to look at the actual code. Maybe log the context as you go into the method to determine whats happening. Editing an Item Fulfillment will trigger the UE regardless if there is detail.