If it's not showing up by following the steps in the support document you posted from, then it's not tied to the Apple ID you are currently logged in with. You either started it with a different Apple ID, or on a different platform so its not actually tied to your Apple ID.
There is no issue with the system. It works as designed and will show all subscriptions tied to the Apple ID currently logged in. The fact its not there is not an issue with the system.
click here-> If the subscription that you want to cancel is not listed - Apple Support