Order Viewer not working

Hi, 

I've been having problems recently with the Load In Order Viewer button on my Woocommerce site. When I click on it, it's stuck on "Loading data..." and I'm getting the following error on the console:

Here's another screenshot of what's sent over the network:

There was also a case where I get an empty order_data json body. But I could not replicate it. I'm not sure if that's relevant, though. 

I tried disabling the third-party libraries, but with no success. 

Here's the link to the site that's problematic:

https://cheapnextdaywristbands.co.uk/product/personalised-wristbands-next-day-delivery/

Please let me know what other information you need. 

Thank you.