Amazon Shipment Check In

I’ve been selling on Amazon for over 11 years. It seems that Amazon employees are not good at counting. I manufacture and sell my own products therefore I pack and label them to go to Amazon. Once in a while they say I shorted the amount I claim to have sent in. In fact a recent shipment of 100 units was received at Amazon as 72 units, 28 units short! I get the feeling there are thieves at Amazon that steal product to sell themselves elsewhere like on ebay. Has anyone else had this same experience?