Question:

The page should show the multiple select, but it does not at all in the GRID mode.
If I switch to LIST mode, it shows the Add All Products, but it never shows the checkbox next to the product.
It did work in LUMA theme, however it showed 2 of everything: 2 Add All boxes, 2 product checkboxes, and 2 quantity fields.


Answer: 

The reason might be due to the button Add To Cart in your theme is missing the class “tocart”, which make the module cannot find the button to add the checkbox and quantity box.


1. In case button Add All To Cart has already displayed but the Checkbox and Quantity box have not:
- Please check whether the block item has class “product-item” or not - if the block item hasn’t have yet, it is suggested that you should add the new or present class of the item into this line $(this).find('.product-item').each(function () { of the file: Bss/AddMultipleProducts/view/frontend/web/js/addmultipleproducts.js

- Please check whether the button has class “tocart” or not -  if the block item hasn’t have yet, it is suggested that you should add the new or present class of the button into these lines: $(this).find('button.tocart').before(checkbox_addmuntiple);
$(this).find('button.tocart').before(qty_addmuntiple);
of the file: Bss/AddMultipleProducts/view/frontend/web/js/addmultipleproducts.js

Could you please refer the screenshot below for reference?





2. In case button Add All To Cart does not display, could you please double check the config class in the backend?


Please note that it's just the solution for your reference.

For more information about product, please refer Add Multiple Products To Cart for Magento 2.
If you need any further assistance, please feel free to contact us.
Please visit our site for more useful Magento 2 Extensions: https://bsscommerce.com/magento-2-extensions.html