I have a Sitecore site and on 2 of my CD servers, `Url.Action` returns an empty string. This works locally and on 9 other servers ranging from dev to prod, CD and CM.

Deployment automation ensures that the exact same `web.config` is deployed to all environments; ditto for all other configs.

My controller inherits from `SitecoreController` properly. This is not isolated to a certain controller or action, this happens with all controllers and actions.

What would make `Url.Action` return an empty string in one environment and not others, with identical code?