Ziggurat boss becomes unkillable - with steps & tests

Normally, that boss goes :
1) Boss can be attacked up to ~75%
2) Boss becomes invincible, then spawns the Lich add #1
3) Once Lich add #1 is dead, boss can be attacked up to ~50%
4) Boss becomes invincible, then spawns the Lich add #2
5) Once Lich add #2 is dead, boss can be attacked up to ~25%
6) Boss becomes invincible, then spawns the Lich add #3
7) Once Lich add #3 is dead, boss can killed

The bug is :
After 1), if you have lingering damage (in my case, vaal lightning strike) and Lich #1 dies instantly, Catarina will skip step 3) and spawn the step 4) Lich #2.
The fight then proceeds normally, except the boss has 50% remaning HP once Lich #3 is dead, an can only be brought down to 25%. She then does the animation she would always do to spawn a Lich, except there is none left, and remains invincible forever.

I this happens 100% of the time, and I reproduced it more than 10 times this morning.

I did a few more tests :
- This happens whether the boss is delirious or not
- If you reduce your damage so that Lich #1 survives long enough for Catarina to attack you, the bug does not happen.

I can confirm this. Happend to me 5 minutes ago as well. 2 liches spawned at the same time and then she was invincible at 25% Hp.

same situation here, 2 liches spawned at the same time and then she was invincible at 25% Hp.

exact same thing happened to me, triggered by high dps

Same here

Same

Same here, happened to me 4 times today.

Same happened to me, very annoying.