Subscription was stopped by BA during Daily Billing Process due to an overusage of one of the resources. Provider switched resource control type to "Controlled by External System", in order to manage resource by OA and eliminate subscription stopping. Or the customer decreased the usage of the resource, so that it is not overused anymore. It is expected that the subscription will be started automatically with the next daily billing, but that did not happen.
The situation is caused by internal issue with ID #PBA-48455 ("If a subscription was stopped because of overusage, it will not be started until it's next billing date").
Upgrade to BA 6.0.x or later where the bug is fixed.