To try and resolve the issue follow the steps below to reconnect and retry marking the orders as shipped:
Reconnect Shopify
Select the Settings tab.
Under eCommerce select eCommerce Integrations.
A list of your current integrations will appear, select your Shopify integration.
At the bottom select Reconnect Integration.
It will redirect you to your Shopify site (You may need to log in if you are not already logged into your Shopify account.) and then return to your XPS Ship page.
After reconnecting you can return to the History/Track page to retry marking the order(s) as shipped.
Retry Multiple Shipments
Select the History/Track tab.
Select Filter/Export on the top right.
From here select Only show orders with eCommerce integration errors and click Search.
After selecting Search you will see a list of all your shipments with integration errors and within the date range.
Click the option to Retry Marking all Orders as Shipped at the top right.
If successful, the update errors should change to say Updated.
Note: Any orders already manually marked as fulfilled will not update since they have already been marked as fulfilled.