in the clip we can see that we get platinum but at the time to see the achievement it didn't complete and in the image theres the title triumph.
https://imgur.com/a/rvzB7em
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Hey there, Thank you for reaching us. Were you able to complete the encounter within the bonus time and defeat all enemies, including Tormentors? Players are getting the triumph and we confirmed on our side that there's no issue about it. The Platinum time is just a bonus to help you get a higher score.