The error shown in the console is:

The resource from “https://static.zohocdn.com/zmail/zm/newContactsChange11/js/main.js” was blocked due to MIME type (“application/json”) mismatch (X-Content-Type-Options: nosniff).

This should be fairly self-explanatory, and easy to fix.

It's been a problem for a bit, but thought I should report it, as it's obviously not triggering any errors with dev ops monitoring

When fixing this error, a perhaps a test to check that the Contacts interface successfully loads could be added.

This, along with unit tests to check a contact can be added, edited, deleted, etc might be considered an absolute minimum for any production code.