Inventory misplaced means just that. Have you ever set your keys down and forgot where you put them? Now imagine you have a Fulfillment Center with football fields of inventory. Sometimes things get misplaced.
Amazon will auto-reimburse you if the item is missing longer than 30 days. There is no point contacting Seller Support days after they go missing, they will ask you to wait 30 days. While you CAN spend your time reconciling everything if you really want, the automated system works pretty well. The only time you would need to contact Seller Support is if something has been missing greater than 30 days and you haven’t been auto-reimbursed.
Keep in mind it might take a few days to process the reimbursement, so I wouldn’t contact until 35 have passed. Otherwise, you are wasting your time.