Thank you
Here is what I found, hope you find it helpful! 
Questions surrounding lost or delayed inbound shipments are some of the most frequent forums posts. Fulfillment centers see delays when there is a large volume of arriving shipments at once, particularly during peak times like the holiday season. So, what can you do if you have a lost FBA shipment?
The first thing to note is that the receiving process takes time. The shipment events tab allows you to follow along with updates on your shipment’s journey from shipment creation to it’s addition to your inventory. Your shipment will need to be delivered, checked in, and received which will take at least six days, but often longer. To ensure quick and accurate receiving, ensure that you have followed all packing, labeling, and shipping requirements.
After we have confirmed receipt of all units, or your shipment has been open for more than 90 days, the status will change to “closed.” Around this time, if there were any quantity discrepancies, you can request investigation and reconcile your shipment. On the help page linked, you can check if your shipment is eligible for investigation. This is also available on the Contents tab of the Shipment summary page.
If your shipment is not eligible for investigation, it may still be processing at the fulfillment center. If it is eligible, you will need to provide a couple of documents to launch an investigation.
Proof of inventory ownership including the date of purchase/packing, product names, and quantity such as
- a signed packing slip if you are the manufacturer with the shipment or purchase order ID
- an invoice from a supplier including the full name and address of the invoice issuer and of the purchaser
Proof of delivery, which, for LTL or FTL shipments, will be the bill of lading showing
- the number of boxes in the shipment
- the total weight when picked up by the carrier
- an Amazon stamp confirming the shipment was received and signed for at the fulfillment center
If you believe your shipment has been lost on it’s way to the Fulfillment Center, provide the drop-off receipt or proof of pick-up from the carrier.
After you have submitted your request, a case with Seller Support will be created. You can view updates and communicate with the team via your case log.