prestashop 1.7.6.4 presta native module cart quantity update issue fixed here
open this source file under module PS_Cart module folder ps_shoppingcart.js then add these 3 lines after the line 45
if (event && event.resp && event.resp.hasError) {
prestashop.emit('showErrorNextToAddtoCartButton', { errorMessage: event.resp.errors.join('
')});
}