Best Offence (Kalphite King CA)

Hopefully someone out there can add some clarity to help with this, because it seems like this CA has given lots of people trouble.

For this task, players have to trigger KK’s Immortality ability but using a specific ultimate ability based on its current phase (melee, magic or ranged) when the boss is under 35k hp. After triggering the Immortality ability, players must then defeat KK after it heals back up.

There are multiple problems with this. Sometimes using the ability triggers Barricade and not Immortality. I’m fine with it being a 50/50 chance to trigger one or the other, but often, NOTHING is triggered at all.

Additionally, sometimes you will get the chat message that Immortality has been triggered, but then he doesn’t actually heal, and the achievement does not complete. My friends and I completed this task probably 8-9 times last night which was no easy feat considering the RNG to even get him to trigger Immortality at all. Can anyone explain, or help explain why the achievement is not actually completing? I would really appreciate it!!!