After looking into this, there are some product variants in your shop which have fields for the “weight_value” as null, when they should be defaulted to 0.0 or contain a valid value. I’m not sure how exactly this has happened, but if you look at the product variants on those subscriptions and perhaps set their weight to 0.1g as a test, then save them, and see if that resolves your GraphQL errors?
I will still report this as a bug needing improvements for both the error being raised and why values are being stored as null for weight instead of 0.0 to help prevent this issue in the future.