If a task attempt fails in the ASSIGNED state, e.g.: container launch fails, then it can disappear from the job history. The task overview page will show subsequent attempts but the attempt in question is simply missing. For example attempt ID 1 appears but the attempt ID 0 is missing. Similarly in the job overview page the task attempt doesn't appear in any of the failed/killed/succeeded counts or pages. It's as if the task attempt never existed, but the AM logs show otherwise.