I added a Target tool and my previous page load rule implementation broke, why?

If the mbox.js code was previously deployed via a global page load rule, adding a new Target tool to the property or changing the configuration of an existing Target tool could break this implementation method. This occurs because the tool deploys another instance of the mbox.js when utilizing either of the available automatic configuration options, or the Manual > Hosted by Adobe configuration option.

Essentially, you must ensure only one instance of mbox.js code is being deployed; so, it's vital to test the new tool configuration in staging and ensure only one instance of mbox.js is deployed before publishing these changes to production.