Doriyani in citadel not transitioning into mech and instagibing character.

I got doriyani in the stone citadel down to 0 health. He never transitioned into his mech. He then instantly killed me with an electric attack similar to emperor palatine where he pinned me to the floor and cooked me with lightening. It reminds me of the issue when you drain the health of the 4th trial of sekhema boss too quickly and it doesnt finish the timer from the 1st round of having to stand on his time bubbles. This leads to him mistakenly 1-shotting you when he shouldn't as you completed the mechanic.
The attack doriyana killed me with isnt listed on his boss page on maxroll, it isn't in any stream of anyone defeating the boss either. it drained nearly 4000 energy shield and 1,600hp instantly and I cant find any reference to this attack from any source online. Killing Doriyana too quickly seems to bug him out, cause the citadel to become unfinishable and leads to him killing you with an unavoidable 1 shot kill.