Assuming you see the request being made to Target and a response being returned with offer content, the most likely cause is that the HTML structure of the page has changed and your CSS Selector no longer exists. You can check if this is the case as follows:
i) If you're using the Visual Editor, you can check to see what the selector is by clicking the i icon:
ii) Go to the page where your test should run, open Developer Tools, and enter
document.querySelector('<copy element value from vec>')
e.g.
document.querySelector('HTML > BODY > DIV:nth-of-type(2) > DIV:nth-of-type(2)')
If your CSS selector isn't valid then you will see a null value
If that is the case then you need to update the CSS selector in the Target Visual Editor