Prevent WooCommerce from emptying carts after the order limit has been reached — https://wordpress.org/support/topic/cart-empties-when-limit-is-hit/

limit-orders-do-not-empty-cart.php

<?php
/**
 * Plugin Name: Limit Orders for WooCommerce - Prevent Empty Carts
 * Description: Prevent WooCommerce from emptying carts after the order limit has been reached.
 * Author:      Nexcess
 * Author URI:  https://nexcess.net
 */

/**
 * Prevent WooCommerce from removing non-purchasable items from the cart.
 *
 * Limit Orders for WooCommerce marks all products as non-purchasable once the threshold has been
 * reached, but WC_Cart_Session::get_cart_from_session() will remove any non-purchasable items from
 * the cart.
 *
 * This callback lets items be purchasable (unless they were being prevented for some other reason)
 * for the sake of loading the cart, but will still disable "Add to Cart" buttons across the site
 * until the next interval starts.
 *
 * @ticket https://wordpress.org/support/topic/cart-empties-when-limit-is-hit/
 */
add_action( 'woocommerce_load_cart_from_session', function () {
	// Limit Orders registers the filter callback at a priority of 10.
	if ( 10 !== has_action( 'woocommerce_is_purchasable', '__return_false' ) ) {
		return;
	}

	// Temporarily remove the filter.
	remove_filter( 'woocommerce_is_purchasable', '__return_false' );

	// Once the cart is loaded, put the filter back in place.
	add_action( 'woocommerce_cart_loaded_from_session', function () {
		add_filter( 'woocommerce_is_purchasable', '__return_false' );
	} );
} );