I'm not sure what more to suggest. Recommend creating a test user, subscribing them to your plan, then within CBSubs > Subscriptions modify the subscription date, expiration date, and set status to expired. Next login as that test user to see if it allows you to renew. This should allow you to reliably retest the scenario. If you can confirm then begin reviewing the configuration of your plan carefully as something is blocking the renewal (likely some sort of access permission).