Etsy will not save a listing that uses a calculated shipping profile unless the listing has a weight. That is because Etsy works out the shipping cost from the weight. Shuttle shows this error when Etsy turns a product down for this reason, and the product is not saved on Etsy until it has a weight.
When the calculated shipping profile error appears
The calculated shipping profile error usually appears when Shuttle updates a product that is already on Etsy, or changes its status. Etsy rejects the change if Shuttle has no weight to send for the product and the Etsy listing has no weight of its own.
The Weight handling setting can also cause the calculated shipping profile error. When Weight handling is set to Remove weight data to fix Etsy save errors, Shuttle clears the weight from Etsy listings when it updates their dimensions and weight. A listing with a calculated shipping profile cannot be saved without a weight.
Where Shuttle gets a product's weight
Shuttle uses the first weight it finds for a product, checking these places in this order:
The weight of the product's first variant in Shopify
The Shopify metafield you named for Weight in Settings > Products > General, under Shopify metafields
The Default weight in Settings > Products > Shopify → Etsy, under Dimensions & Weight
If Shuttle finds no weight in any of these places, it keeps the weight already on the Etsy listing. If the Etsy listing has no weight either, Etsy rejects the product.
How to fix the calculated shipping profile error
Go to Settings > Products > Shopify → Etsy and find Dimensions & Weight.
Set Weight handling to Send weight data as usual (no changes).
Give the product a weight. You can add a weight to the product's first variant in Shopify, or enter a Default weight and choose the matching Weight unit. Shuttle uses the Default weight for any product that has no weight in Shopify.
Click Save.
Update the product on Etsy again and select Dim. & Weight as one of the fields to update.
You can also add a weight to the listing directly in Etsy. Shuttle keeps that weight when it has no other weight to send.
For more on weight and dimension settings, see Ensuring Accurate Product Dimensions & Weights During Transfers.
To check which shipping profile your products get, see Ensuring Products Are Assigned the Correct Shipping Profiles.