Stutter on Mouse-Move after ~ 40 minutes of gameplay

Hello, here are my specs:

CPU: AMD Ryzen 5 5600
RAM: 16GB 3200 MHz
GPU: Asus Radeon RX 7800 XT
Ethernet: LAN (250mbit)

OS: Kubuntu 24.04.1
Kernel 6.8.0-51-generic (standard)
Mesa 24.3.3 (from kisak-mesa repo)
Wayland-Session (by default)

my problem:

while in the game, after ~40 minutes of gameplay, my screen starts to stutter horrible, but only when i move the mouse on the screen. Fixed fps at 60 then go down to 20-30, when mouse doesn't move the fps stays at 60, even when the character (Infernalist-Witch) is moving after mouse-click.

tried to put all settings to low
tried to switch from vulkan to dx12
tried to change vulkan-session to x11-session
tried to disable shader-precaching and allow shader-cashing in background
tried different versions of proton (e.g. proton-ge from 9.19 to 9.22), also
proton-experimental and non specific proton

nothing of the above changed anything. i'm out of ideas now. can you help with this please?

Greetings and thx in advance, Wursti

Edit: I'm talking about Path Of Exile 2 here :-)