[Linux] Bizzare performance; gamble if it runs well or not.

Validation

• I have checked the Issues page to see if my problem has already been reported
• I have confirmed that this bug does not occur in the original game running on original Xbox 360 hardware

If you have DLC installed, please specify which ones you have.

• Apotos & Shamar Adventure Pack
• Chun-nan Adventure Pack
• Empire City & Adabat Adventure Pack
• Holoska Adventure Pack
• Mazuri Adventure Pack
• Spagonia Adventure Pack

If you have mods enabled, please specify which ones you have.

I disabled all mods just to see if this issue persists, and it does.

If you have codes enabled, please specify which ones you have.

Disabling all codes also causes this.

Describe the Bug

There's no clear way to go about this, sometimes the game just runs abysmally in intense areas. An example is in Empire City's village, when looking towards the level gate, the game runs at around 30 FPS, but turning the camera around runs at 60 FPS. However, this is randomly dependant on when I launch the game. Sometimes, the game runs at 60 FPS just fine in all areas. But then I close it, do somethings, then come back to the game, and it consistently runs poorly. If I keep closing and re-opening the game, I might eventually see it run at 60 FPS again.

Screenshots

Here's an image of the performance graph as I rotate the camera in Empire City.

Same graph but it's been looking at the scene long enough to fill up the whole graph.

And here's the performance graph when everything is running correctly; as I said it's random when the game decides to work or not. This is the exact same scene in Empire City.

Provided is also a screenshot of LACT, showing my GPU's performance. The dips in the power usage indicate the game lagging, meaning the GPU is deciding to do less work, for unknown reasons. My CPU isn't being hammered by the game.

And here's LACT when the GPU is actually rendering the game at 60 FPS.

Specifications

Fill out the following details:

• CPU: AMD Ryzen 5 5600G (iGPU is disabled in BIOS, game does not report it being used)
• GPU: AMD Radeon RX 6600 XT
• GPU Driver: amdgpu; Mesa 25.0.0 (LLVM 19.1.7)
• OS: Ultramarine Linux 41 (Cyberia) x86_64
• Version: 1.0.2

Additional Context

I have tried various fixes on my end; Using LD_PRELOAD="", doing both amdgpu.aspm=1 and amdgpu.aspm=0 in GRUB, using Cinnamon instead of KDE Plasma (so, X11 vs Wayland; doing X11 under wayland also didn't fix this), using CoreCTRL and LACT to manually set GPU frequencies (memory frequenices can be set, GPU frequencies are ignored for unknown reasons), and closing all other applications doesn't affect the results in any meaningful way.

Reproduce the issue in Empire City's village on Ultramarine Linux 41 with the listed Radeon RX 6600 XT and Mesa 25.0.0 setup, comparing repeated launches and camera directions. Start by reviewing the performance graphs and GPU power readings, then determine a repeatable trigger and verify that the game consistently maintains the expected 60 FPS when the issue is resolved.