Do you have multiple autoresponders for specific ASIN products?
So the email sequences you create in the All Amazon Users group will apply to all of your SKUs, unless you create a new sequence on any of the product group(s). Whenever you set an email sequence in a product group, you override the default one for that product. So you may create an special sequence for a product and use the default one for the other ones.
The process to create a groups for any specific SKU is done automatically during the syncing process, so you don’t need to create groups for your products.