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. Click the Manage Listings button, then click the green edit icon on the channel settings tile.
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.