Do you have the campaign in a program? It has to be in a program to be added to the stream, and only one per program. So if you need to make 9 different campaigns to do A/B testing on 18 different emails, you need to make 9 different programs.
Also, check and make sure that the smart campaign criteria (smart list) is something that will pull the leads in (ex: member of engagement program: prospects, stream: early).
Then be sure and activate the program in the stream.
Hope this helps!