Initiating Ultimatum encounter crashes and exits client - no error message

About 50% of the time when I start the first phase of an Ultimatum encounter, the game staggers for about 1 second immediately after starting it (while he say's his starting-encounter-dialogue), then proceeds to crash and quickly close the game without any error message in-game or in windows. I'm not experiencing any other crashes except this. From reading reddit and forums, there seems to be other players with the exact same problem.

Correction - the crash can also occur in later stages.

Tried with DirectX11 and Vulcan, same issue.

iam crashing about 80% of the ultimatums and it makes me quite sad becouse i like the league mechanic.

Same problem here. As described before, im crashing estimated 50% of the time when starting a Ultimatum and sometimes even on later stages. No error message, just get thrown to the desktop. My game runs very smooth with no crashes and almost always above 100 FPS outside of that. I tried almost every Setting (Vulcan, DX11, Dynamic Culling, Dyamic Resolution, Incursion/Ultimatum Effect, etc.) nothing did work so far. Still crashing after todays hotfix "Fixed a common client crash that could occur during Ultimatum encounters."

Its really really frustrating :( I also died around 20x because of it...

same here i'm runing game in 3440x1440 resolution, windowed fullscreen 1 on 4 ultimate crash a game on start when just click on skill on late stage got one crash

still no changes after the recent patch. crashing again in ultimatum, no error message, stagger for 1-2 seconds, then dropping to windows. happened just now, in my first ultimatum in my first map today. this is becoming a really bad experience now and it really needs a fix. seen several people complaining about the exact same thing as well.

also happening a bit further into the ultimatum encounter now, not only directly after pressing begin

same happening to me, sometimes i get this error message about insuficient memory, C++ library something...
already reinstalled the whole library, tested all settings , cant fix, cant play the league mechanic...

Same here. I played Bladefall/BladeBlast Assassins. The crash is only occurring in Ultimatum. looks like Bladefall is the dominant cause. It seems to be different for each encounter, but it may occur continuously or not for a while.

I tried the following changes, but nothing changed.

-Formatting Disk, Reinstall OS
-Deactivate Overclock
-Change Resolution
-Change API
-Switching Vsync/Dynamic Culling/Dynamic Resolution
-Change Window Mode
-Most Graphical Detail combinations by changing level
-Switching Client Language

This is my Event log from last crash