The log shows that it fails during text completion too. This is some sort of mystery OS/driver/backend issue, since the only thing the game does differently between sending requests to Qwen and sending requests to Gemma is that it launches the backend with SWA enabled on Gemma.
You could try letting the game load the model, then killing the hidden Kobold process after it's done loading the model, and run this command in the StreamingAssets folder to "switch out" the backend process for one without SWA:
./koboldcpp-linux --model "Gemma-4-Sparse.gguf" --usevulkan --gpulayers -1 --quiet --multiuser 100 --contextsize 4096 --skiplauncher --port 5003 --nofastforward
If SWA isn't what causes the problem, I'm out of ideas. It's difficult for me to debug what's happening here because I don't have an AMD system to reproduce the bug with, if that's even the cause.