There are four circumstances when a SKU will not sync.
The SKU is not attached to a season code for a season that is set to sync - double check the SKU season, and the seasons set to sync in the shopify configuration is selected.
Advanced > Administration > DC Setting > Integration > Shopify configuration > Edit.
The SKU does not match - Confirm that they all exact match character for character and make sure there are no spaces within the SKU.
The SKU or style is not published in shopify. If the SKU is being hidden, then it will not sync through integration.
In Shopify, go into the products variant setting, check that the Inventory Policy set to Allow Shopify to track inventory
When it’s not tracking inventory it can’t post the Blast Ramp quantities.
Please allow some time between syncs (about 20 mins or so)