When you change the SKU number in ecomdash, can you confirm that your reference ID's are updated as well:
1. Navigate to Inventory -> Inventory Management
2. Click into your SKU number that is not syncing properly
3. Choose the 'Storefront' tab.
4. You will see a reference ID column and a value for each storefront.
Confirm that the reference ID values are set to match each sales channel SKU number exactly.