Temporary fix for Magento 2 bug where invoices for PayPal orders do not have address information attached. This mainly shows up in the grid. See https://github.com/magento/magento2/issues/6438

etc_di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="C3\Magento2Fixes\Observer\AfterOrderInvoiceAddresses">
        <arguments>
            <!-- Pass Virtual Invoice Grid type in observer - must be done in DI as virtual -->
            <argument name="invoiceGrid" xsi:type="object">Magento\Sales\Model\ResourceModel\Order\Invoice\Grid</argument>
        </arguments>
    </type>
</config>

etc_events.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="paypal_express_place_order_success">
        <observer name="c3_fixes_update_invoice_address_data" instance="C3\Magento2Fixes\Observer\AfterOrderInvoiceAddresses" />
    </event>
</config>

Observer_AfterOrderInvoiceAddresses.php

<?php

namespace C3\Magento2Fixes\Observer;

use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;
use Magento\Sales\Model\Order\InvoiceFactory;

class AfterOrderInvoiceAddresses implements ObserverInterface
{
    /**
     * @var \Magento\Sales\Model\ResourceModel\Grid
     */
    protected $invoiceGrid;

    /**
     * @var InvoiceFactory
     */
    protected $invoiceFactory;

    public function __construct(
        \Magento\Sales\Model\ResourceModel\Grid $invoiceGrid,
        InvoiceFactory $invoiceFactory
    ) {
        $this->invoiceGrid = $invoiceGrid;
        $this->invoiceFactory = $invoiceFactory;
    }

    public function execute(Observer $observer)
    {
        $order = $observer->getOrder();

        // Get all invoices attached to order (likely just 1)
        $invoices = $order->getInvoiceCollection();
        foreach ($invoices as $invoice) {
            // If invoice missed address IDs, set from order
            if ($invoice->getShippingAddressId() == null || $invoice->getBillingAddressId() == null) {
                $newInvoice = $this->invoiceFactory->create()->load($invoice->getId());
                $newInvoice->setShippingAddressId($order->getShippingAddress()->getId());
                $newInvoice->setBillingAddressId($order->getBillingAddress()->getId());

                // Save address IDs
                $newInvoice->save();
                // Refresh data in invoice grid
                $this->invoiceGrid->refresh($order->getId(), $this->invoiceGrid->getOrderIdField());
            }
        }

    }
}