I’ve done some more testing and I’m finding this primarily happens during the following scenario:
We build campaign landing pages on our website platform across all of our country instances. While these are in development (and obviously not published yet), we are building Marketo programs to support all of these landing pages. We build a master program (with assets and smart campaigns) in our global workspace and then once complete, we clone them to the other 21 workspaces. This also includes changing the URLs of the web pages within the smart lists/campaigns to the country-specific programs. Keep in mind, these pages aren’t published yet and therefore have a red line underneath (which is expected since the page hasn’t been indexed by Marketo yet). Once we publish all of the campaign pages (and physically visit each page so that Marketo can index them), we revisit the smart campaigns to activate them. That process includes ensuring the red line is removed. And this is where we run into issues – causing us to constantly go back and forth; and try different techniques to finally have Marketo view the URL as valid.