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.