@Stefano Cairoli reminded me of my vow to update this with the release of the stochastic estimator. @Sarah Matthews did a fantastic job building it! 

I thought about it a bit. There are additional possible explanations depending on deployment topology and journal purge settings: 

• Mirror member is offline
• Backup failed
• %SYS.Task.PurgeJournal is suspended/disabled/deleted

Great article! I like the code snippet for more advanced automation of managing transactions.

I often suggest this query to find transactions that are open longer than is suitable for operational stability. 

SELECT * 
FROM %SYS_Journal.Transaction_List() 
WHERE DATEDIFF('s', StartTime, NOW()) > 60