Hi Jack,
Your customizing and understanding are correct. yMKT behavior is also correct. yMKT have some campaign categories such as (1) Normal campaign including once and periodic, (2) Newsletter like weekly, monthly and your specific period, (3) Trigger-based campaign.
In normal campaign case, you don't need to take care of any configuration after initial setup. because, target members of the campaign is decided by your segmentation and user's general opt-status.
Howerver, If a consumer doesn't want to subscribe weekly newsletter but wants monthly newsletter, yMKT cannot judge whether sent each newsletter or not without more specific user's consent. Thus, you need to register the opt-status with initiative ID like 13, 101 for monthly newsletter through registration of an interaction based on user's consent.
This behavior depends on your executed campaign category (A1,A2 or NL).
Now going back to your result, yMKT couldn't find the opt-status record with initiative ID from MP_ROOT, the result was failed.
Regards,
Shimon