Hey @animesh, WorkflowTaskTimedOut might happen in various failure situation. The most common is when a worker restarts which has workflow executions cached. Any new event for those workflow will result in a WorkflowTask being scheduled on host specific tasklist, but since there is no poller on the tasklist it results in a WorkflowTaskTimedOut and new workflow task getting scheduled on global tasklist so another worker can pick up the WorkflowTask.
Some other useful forum posts which goes into more details about WorkflowTask: