Is there a way to generate an alert when a process has zero tasks for a set duration of time?

ok, first you got several responses to handle real errors that should be handled by an OOTB alerts. If you are still looking for a solution, following should help:
create a process report that lists number of active tasks. use a!queryAnalytics function to get number of active tasks (including from sub process models) by passing parent process model as context. run this as daily schedule job to send alert report to application support team.

> What we know: we know how many tasks are associated with a given process, so we can cross check against that [ (if activeTasks == 0 && completedTasks < totalTasks) SEND ALERT!] ....are you aware of any function that can check the active task count?
- There are ways to do this. As suggested by other practitioners, create a daily/weekly scheduled processes to check and alert the appropriate user/admins etc.

 

My concern is this "What if the process didn't fail, it just stalled out for whatever reason (sometimes for no reason....just happens and you need to restart the task)." There should be no unattended node (any node/task that is not User input task, or has a form for the user to act on) that runs for more than 60 mins and doesn't move the process to error (paused by exception). You have to find the root cause and fix it. 

 

From documentation: "The activity must alost complete within 60 minutes or the process will pause by exception."

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