got answer:
Did you check the error messages on your store? Amazon limits your account to 2000 request per hour to their api for new members. They don't want someone calling their api 10,000 times a hour and never actually making any sales as it costs them a lot of money in bandwidth usage. So new members get capped at 2000reuqest per hour and if in one hour you go over 2k, the items will go out of stock because amazon.com won't update it, after the hour they will update. So if you have a lot of stores with each having hundreds of products then that could be a issue. I recommend bringing down the amount of products you have or let them add naturally over time. Amazon will increase your limit once you account starts selling items.