When app shows no content, 99% of the time issue is on a client side and has nothing wrong with the app. There could be several reasons for it.
If you are not on up to date chrome version or if you have browser cookies disabled, shopify apps might fail to load. This is a client specific to your local browser so first thing you should do is check whether you can load app in another browser.
When app loads in another browser, that means this is definitely issue on your end around a browser configuration. Here are few things you can check.
1. Log out & log back in your shopify admin account
> Log out from your admin & then close a browser. Once you log back in, give it a try loading an app and see if it works.
2. Check whether you are on latest version of browser?
> Most times clients have auto updates off so you might be few versions old. Check whether you are on latest version and if not, upgrade to latest version.
3. Check whether browser cookies are enabled?
> Cookies play important role in any Shopify embedded app. Make sure you have allowed third party cookies.
Follow this guide to make sure you aren't blocking any third party cookies.
If you still can't get app loading, please contact our support at firstname.lastname@example.org with some screenshots.