Please update the plugin to the latest version which is v2.2.1.
1. You have to select Dokan shipping from the shipping method option. Pelase navigate to WooCommerce->Settings->Shipping. At first enable Dokan shipping then in the shipping method select the method as Dokan shipping. If any thing is now working after then then provide a screenshot here.
Seller can also override shipping from their product edit page. If seller want to override shipping cost for a product then he can override it from product edit->shipping. This is not bug. Please check those feature correctly. Seller can set shipping rate from his dashboard. He can also override it for a single product.