Bugged achievements Hidden Arcana
You need to tag the bosses (even if it does 0 damage) for the achievements to register. I see you are in there with at least one more person. If he did all the work for you, this is probably your issue.
1st person worldwide to reach 35,000 achievement points.
I tried a few methods including hitting the boss. The second boss with the colour attunements, I took 50% of his health and still no achievement. For the boss that needs to be brought down to 0 from 75%, i hit multiple adds with the fragile buff. This is the sixth time that I replayed the content with the same result, each time trying something different and each time the achievement not being given after the boos was compelted, while the buff remains on the bar.