Magento 2.1 – Fix Shopping Cart Item Removal Issue

Below is the solution for Magento 2.3.5

Please override Failure.php and change public function as below,

public function execute()
{
    $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
    $_checkoutSession = $objectManager->create('\Magento\Checkout\Model\Session');
    $_quoteFactory = $objectManager->create('\Magento\Quote\Model\QuoteFactory');
    
    $order = $_checkoutSession->getLastRealOrder();
    $quote = $_quoteFactory->create()->loadByIdWithoutStore($order->getQuoteId());
    if ($quote->getId()) {
        $quote->setIsActive(1)->setReservedOrderId(null)->save();
        $_checkoutSession->replaceQuote($quote);
        $resultRedirect = $this->resultRedirectFactory->create();
        $resultRedirect->setPath('checkout/cart');
        //$this->messageManager->addWarningMessage('Payment Failed.');
        return $resultRedirect;
    }
}

could you explain more your task ? the customer 1 has to keep his quote and items ? and the customer 2 just have the same items than the customer 1 that's it? In this case just use the addProduct method which take 2 parameters ($product, $qty).

Get the items from customer 1's quote. Loop on it, and add product to your customer 2's quote.