I've been trying for over a year to get ads to show on one of my channels and I've done everything by the book. All I get is the in-house ads from Roku which makes me look like a rookie. If the channel is side-loaded from home I get random ads, but never after publishing...
the fact that you were seeing test ads (that's all these were) means that technically your app was set up for displaying ads. Such ads still showing on published apps was casing great confusion and so in August the practice was terminated.
The organizational part was missing though - Roku's ads department must approve channel as ads display supplier and start sending ads to it. This is a part i cannot help you with and recommend contacting partnerSuccess at roku.com for the terms and requirements. Alternatively, you can bring your own ad feed to the app through other sources.