Which version of WC Vendors, WC Vendors Pro and WooCommerce are you using?
Would you share your WooCommerce System Status? (wp admin > woocommerce > system status)
In my testing I am not experiencing any of these issues..
The only alteration made recently to the vendor coupons was to change so that free shipping could be used with the coupons. Otherwise, I will check to see if anything else was altered, but I do not believe so.