When you assign a quantity to a product within an ASN, you are still able to book in beyond that quantity.
Idea to resolve Problem
Add a cap to ASN quantities which will prevent more than the expected quantity being booked in. Should you wish to book in more of a product, then you would have to update the quantity in the ASN. This would help to reduce stock discrepancies caused by issues when scanning.
Agreed, especially when some integrations like unleashed don't work if you over book in an ASN