Add Role input field doesn’t populate available roles anymore other users than Administrator, as it has done that before. No known changes made and no new plugins installed. Shop Manager can’t give now additional user role for WooCommerce Customer.
This issue is related to the WooCommerce plugin update. Starting from v. 3.4.6.
shop_manager role can edit just users with ‘customer’ role by default.
If you wish that more roles will be available for shop_manager you can use custom filter as described here.