Unable to re-trigger or test one of the Robotic Tasks

Question

I have many robotic tasks, all of them runs when triggered either from process or by Re-execution or By TEST button, but one of the Robotic tasks which was executing previously has stopped triggering from process model, the process model gets stuck at the robotic tasks node without any errors and fails with timeout after long time. Re-execution of the previous instances is also not triggering any new instance for this robotic tasks alone.

Shubham Aware · Answer

Your issue is most likely a stuck/queued robotic task or no available robot, so the process stays active and times out after 96 hours. https://docs.appian.com/suite/help/26.3/Execute_Robotic_Task.html#runtime-behavior Also, Verify the concurrent execution limit setting on that robotic task - if it's set to 1 and a previous instance is stuck In Progress, new ones queue indefinitely, which matches your exact symptoms (no error, just hangs then times out). https://docs.appian.com/suite/help/26.3/rpa-9.22/configure-run-time-settings-tab.html 
 https://docs.appian.com/suite/help/26.3/rpa-9.22/robotic-task-execution.html

Harsha Sharma · Answer

If An execution instance is not getting created it is weird indeed and I have never faced this with my limited experience with RPA. I can suggest few things as of now, that you can try. 
 
 If recently any modifications are made to the Robotic task, then revert it back to the version before and try to run the task. 
 If no modifications are made, then see if recently you had RPA upgrade/any hotfix deployments done that might have as regression impacted this behaviour. Appian Support team should be looped in on this issue in this case for resolution. 
 The Robotic task design, whether its in a loop or a subtask of another robotic task etc might be impacting the debugging. As a note, The debugging execution automatically pauses at the beginning of the Setup and Main sections. So go through this documentation here to debug the robotic task with various debugging options available and try to find the root cause. 
 
 If none of the above work then better to reach out to Appian Support to investigate the matter.