My Events Triumph is showing a constant 'new' (+) notification, despite the fact that I have gone through and clicked off all of my earned Triumphs. In what I'm certain is a related issue, my Crimson Days triumphs (which I'm suspecting I did NOT click off during the event) have disappeared, despite having earned at least two Crimson Days triumphs.
This is a Known Issue. Bungie says before the Events that unclaimed Triumphs will be removed. With that, there came the error that you seem to have new Triumphs, but as these have been removed, it will always show. You will have to wait until they fix this issue. In the meantime, try to ignore it.