This is Rae from Shopify. Thanks for reaching out about your Facebook Marketing app, and welcome to the Community!
I'm sorry to hear about the troubles you're having with loading this app in your admin. Does this same issue happen on multiple browsers? To test this, please try to login to Shopify from several different browsers - like Chrome, Safari, or Firefox - and let me know if the same issue happens across all those browsers.
Equally, I recommend clearing the cache on the browser you're using to see if this resolves the error. In some cases, browsers can cache errors like this, and once the cache is cleared, the errors may stop occurring.
In the meantime, please make sure that your business meets the requirements of using the Facebook Marketing app, and that your page is set up according to the settings outlined here, too. In particular, it's important to ensure that your Facebook business page is published, and that your Facebook account has an 'admin' role on that page. You can read more about changing the page roles on your Facebook business page here.
Keep me posted on how this troubleshooting goes. I look forward to hearing back from you!