Occasionally, and for various reasons, your products may end up in the stranded inventory section in Seller Central.
There could be a host of reasons for this but usually, it's because the listing is missing some sort of information and thus Amazon deems the listing incomplete and moves it to the stranded area.
Here is how you find out the reason typically for it being stranded without having to submit a support ticket.
Navigate to Inventory > Fix stranded inventory
Then simply look for your product and find the reason it's stranded and work to fix it