Severe CPU frametime spikes in Heart of the tribe level (Linux / Vulkan / AMD)

I’m experiencing severe CPU frametime spikes and FPS drops in the Heart of the tribe level, even without monsters remaining.


CPU frametime jumps to 50–60 ms
FPS drops to 15–25
GPU is not saturated
VRAM usage is normal

OS: Ubuntu Linux
Game version: Steam / Proton
Renderer: Vulkan
GPU: AMD RX 7800 XT (RADV / Mesa)
CPU: 5800x3d
Resolution: 2560×1080
FSR enabled
Dynamic resolution enabled (target 60 FPS)

i tried these options, but no effect,
Shadows: Low
Global Illumination: Off
Water: Low
Number of Lights: Low
Bloom: 25% (minimum allowed)
Dynamic Resolution: On
Dynamic Particle Culling: On
Dynamic Culling: On
VSync: Off
Triple Buffering: On (forced by Vulkan)

Screenshot:

screen :

https://imgur.com/a/nqUAfbK

Without a confirmation of the issue being reproduced on a supported Operating System, this bug report is likely to be discarded as an issue with the CPU scheduler unique to unsupported OS.