we had a job fail due to a reducer failing 4 times. Unfortunately the job history UI didn't show this particular failed reducer which lead to confusion as to why the job failed.
This reducer failed to launch all 4 task attempts with a Token Expiration error and the jobhistory file only gets an event when the task attempt transitions to launched. The webapp JobInfo object only counts the task attempts in the jobhistory file to display under the "Attempt Type" table, so since this task didn't have an attempt with it, it did show it on the UI.
We need to reconcile the task list with the task attempts or also shows more stats for the tasks vs task attempts.