Compatibility Report

Name of the game: Bellwright
Steam AppID: 1812450

System Information

Proton versions tested (all crash)

• GE-Proton10-34
• Proton Experimental
• Proton Hotfix
• Proton 9.0

Launch options tested (all crash)

• No launch options
• force_vk_vendor=-1 DXVK_ASYNC=1 gamemoderun %command%
• WINE_LARGE_ADDRESS_AWARE=1 %command%
• WINE_SIMULATE_WRITECOPY=1 %command%
• WINE_SIMULATE_WRITECOPY=1 PROTON_DISABLE_KERNEL_WRITEWATCH=1 %command%
• ulimit -n 524288 && %command%
• %command% -threads=8
• %command% -gc.TimeBetweenPurgingPendingKillObjects=120

Issue description

Game launches and runs for approximately 2-3 minutes before crashing with EXCEPTION_ACCESS_VIOLATION in a background/foreground worker thread. Crash is 100% reproducible regardless of Proton version, launch options, or fresh prefix.

Important observation: The lower the graphics settings, the longer the game runs before crashing. At lowest settings the game runs noticeably longer. This strongly suggests a memory/VRAM budget issue under Proton.

Previously worked: Game ran for 200+ hours on Bazzite with an older kernel without any issues and no special launch options required.

Critical log entries — Crash 1 (Background Worker)

[2026.03.28-09.39.54:588]LogMutableCore: Failed to keep memory budget. Budget: 5120, Current: 8713, New: 1450
[2026.03.28-09.39.54:598]LogMutableCore: Failed to keep memory budget. Budget: 5120, Current: 8704, New: 1565
[2026.03.28-09.40.02:495]LogWindows: Warning: Failed to retrieve TPM device information
[2026.03.28-09.40.02:495]LogWindows: Warning: Failed to retrieve secure boot information
[2026.03.28-09.40.02:495]LogThreadingWindows: Error: Runnable thread Background Worker #8 crashed.
[2026.03.28-09.40.02:495]LogWindows: Error: Fatal error!
[2026.03.28-09.40.02:495]LogWindows: Error: Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x00000021447be0ba
[2026.03.28-09.40.02:496]LogWindows: Error: [Callstack] LowLevelTasks::FScheduler::CreateWorker'::'2'::<lambda_1>::operator()()
[2026.03.28-09.40.02:496]LogWindows: Error: Crash in runnable thread Background Worker #8
[2026.03.28-09.40.02:502]LogExit: Executing StaticShutdownAfterError
[2026.03.28-09.40.02:510]LogCore: Engine exit requested (reason: Win RequestExit)

Critical log entries — Crash 2 (Foreground Worker)

[2026.03.28-17.46.33:034]LogThreadingWindows: Error: Runnable thread Foreground Worker #1 crashed.
[2026.03.28-17.46.33:034]LogWindows: Error: Fatal error!
[2026.03.28-17.46.33:035]LogWindows: Error: Unhandled Exception: EXCEPTION_ACCESS_VIOLATION
[2026.03.28-17.46.33:035]LogWindows: Error: [Callstack] LowLevelTasks::FScheduler::CreateWorker'::'2'::<lambda_1>::operator()()
[2026.03.28-17.46.33:035]LogWindows: Error: Crash in runnable thread Foreground Worker #1
[2026.03.28-17.46.33:045]LogExit: Executing StaticShutdownAfterError
[2026.03.28-17.46.33:053]LogCore: Engine exit requested (reason: Win RequestExit)

Network errors preceding crash

LogNet: Warning: UActorChannel::ProcessBunch: ReadContentBlockPayload failed to find/create object. RepObj: NULL, Channel: 110
LogNet: Warning: UActorChannel::ProcessBunch: ReadContentBlockPayload failed to find/create object. RepObj: NULL, Channel: 133

Secondary error (separate session)

Pure virtual function being called while application was running (GIsRunning == 1)

Root cause hypothesis

1. Proton fails to correctly emulate the Windows memory management that UE5 uses for the Mutable character system (LogMutableCore)
2. TPM/Secure Boot check under Proton triggers undefined behavior in background worker threads
3. The combination causes LowLevelTasks::FScheduler to access invalid memory

Workaround attempts that failed

• Fresh Proton prefix
• All Proton versions tested
• Lowering graphics settings extends runtime but does not prevent crash
• Creating 16GB swapfile + disabling ZRAM (ProtonDB suggestion) — not fully testable due to btrfs filesystem constraints

Related issues

• https://github.com/ValveSoftware/Proton/issues/8270
• https://github.com/ValveSoftware/Proton/issues/9134

ProtonDB reference

https://www.protondb.com/app/1812450