SYMPTOM:
After an upgrade from version 8.x to version 9.x of Strategy, pre-existing subscriptions formerly available on the Subscription Monitor of version 8.x :

are not available on the subscription monitor of version 9.x:

CAUSE:
After having migrated a pre-9.x version project into a new 9.x Metadata shell, the projects still need to complete the upgrade process. If the upgrade process is not complete and subscription tables not populated, subscription will not be available on the subscription monitor on the Intelligence Server.
ACTION:
In order to update an older report subscription into a Strategy 9.x subscription, the Administrator needs to run the 9.x MDUpdateutil.exe (located usually into \Program Files\Common Files\Strategy) on the upgrading metadata:

Once the utility starts up, the user needs to select the project for which schedule jobs needs to be made available and the "Upgrade of History List and Subscriptions" checkbox. At the end of the update History List Caches and Mobile Schedules of the formerly 8.x project will become subscriptions available on the subscription monitor of version 9.x.