Severe simulation thread degradation on Ryzen 9 9950X3D / RTX 5080 in vanilla game

No mods

Fresh SpaceEngineers.cfg

Fresh AppData profile

Fresh Learning to Survive scenario

Space Engineers starts normally but the simulation thread intermittently collapses while rendering remains normal.

Observed behavior:

• FPS remains around 120 FPS
• Simulation Speed drops from 1.00 to anywhere between 0.30 and 0.02
• Menus become sluggish and UI clicks often require multiple attempts
• "Scene too complex" appears in a vanilla tutorial scenario
• The degraded state often persists after an autosave

Shift+F11 examples:

Normal:

• Simulation Speed: 1.00
• Simulation CPU Load: ~2 ms

Failed:

• Simulation Speed: 0.02
• Simulation CPU Load: 3501 ms
• Render CPU: ~1 ms
• Render GPU: ~2 ms
• FPS: ~121

The renderer continues rendering normally while the simulation thread stalls.

Troubleshooting already performed

• Verified game files
• Fresh configuration
• Fresh AppData profile
• No mods
• New tutorial world
• Moved installation from D: SSD to C: NVMe SSD
• Updated motherboard BIOS
• Loaded BIOS Optimized Defaults
• Installed latest AMD chipset drivers
• Tested multiple NVIDIA driver versions
• Clean Boot (all third-party startup services disabled)
• DISM /RestoreHealth completed successfully
• SFC /scannow found no integrity violations
• Windows Event Viewer shows no WHEA hardware errors

Additional observations

• Moving the game from D: to C: improved the initial simulation performance but did not eliminate the issue.
• The issue can occur after an autosave.
• Disk activity returns to idle immediately after autosave while the simulation remains degraded.
• Other simulation-heavy games (Kerbal Space Program, Project Zomboid, Teardown) run normally on the same system.
• Windows CPU, GPU, memory, and disk utilization remain relatively low while the simulation thread stalls.

Attached are the space engineer logs, screenshots of the Shift + F11 menu. I can provide more items like task manager screenshots and resource monitor screenshots as well as a Windows Performance Recorder (.etl) trace.