Here is a vital piece of information that doesn’t seem to be on the web anywhere. Have you ever modified campaign/banner settings and had to wait ages before the effects were visible? Twenty minutes even 😉
Twenty minutes is the default cache timeout, a setting you can easily change while setting up your campaigns.
During testing to you can set the cache timeout value to some low value like 1 second so that effectively the cache doesn’t get used. That’s at Global Settings > Banner Delivery Settings > Time Between Banner Cache Updates (seconds).