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Are you running WC Vendors 1.9.11, WC Vendors Pro 1.4.3 and WooCommerce 3.0.5?
Would you please share your WooCommerce System Status in a reply? (wp admin > WooCommerce > System Status)
Without a little more info, I am afraid I cannot help much.
We did have a bug with these buttons that should be fixed in WC Vendors Pro v1.4.3… if it is the same issue. So please first make sure you have updated to that version of Pro.