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

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.