System instability and file corruption when switching from CSM (Legacy) to UEFI + Secure Boot on Windows 11 (B450 + Ryzen 3600)

Question

Hi everyone,

I’m experiencing a reproducible issue where my system becomes unstable and starts reporting file corruption when switching from CSM (Legacy + UEFI) to pure UEFI mode in BIOS.

System Specs:

• CPU: AMD Ryzen 5 3600
• GPU: AMD Radeon RX 6600
• Motherboard: MSI B450 Mortar Max
• OS: Windows 11 Home (fresh clean install, official ISO)
• Disk: GPT (confirmed)
• TPM: 2.0 (ready and enabled)

Summary of the Problem:

My system is completely stable under BIOS default settings. I can use my PC normally, browse, and play games (e.g., PUBG) without any crashes or issues.

However, the moment I change BIOS settings to meet UEFI/Secure Boot requirements, the problem starts.

Changes made:

• Boot Mode: Legacy + UEFI → UEFI only
• CSM: Enabled → Disabled
• (Secure Boot attempted after this, but instability already appears even before enabling it)

After switching to UEFI:

• Browser starts crashing (“Aw Snap” errors)
• System becomes unstable
• Running sfc /scannow reports: “Windows Resource Protection found corrupt files but was unable to fix some of them”
• Issue repeats even after a fresh reinstall of Windows 11

What I have already done:

• Clean installed Windows 11 Home multiple times (official installer)
• Confirmed disk is GPT
• Confirmed TPM 2.0 is enabled and ready
• Installed latest AMD chipset drivers
• Installed latest GPU drivers
• Fully updated Windows
• Ran DISM: “No component store corruption detected”
• Ran SFC: clean when BIOS is in default settings
• Reverted BIOS to defaults → system becomes stable again

Key Observation:

• BIOS Default (CSM enabled / Legacy + UEFI) → stable
• Pure UEFI mode (CSM disabled) → instability + file corruption
• Issue is fully reproducible

Questions:

• Is this a known issue with B450 motherboards or Ryzen 3000 CPUs when using UEFI on Windows 11?
• Could this be related to memory training, fTPM, or firmware compatibility?
• Why would switching to UEFI mode cause system instability and file corruption on a clean install?
• Are there specific BIOS settings required to stabilize UEFI mode on this platform?

At this point, my system is only stable when using BIOS default settings, which prevents me from enabling Secure Boot (required by some applications like Valorant).

Any help or insight would be greatly appreciated.

Thank you!Hi everyone,

I’m experiencing a reproducible issue where my system becomes unstable and starts reporting file corruption when switching from CSM (Legacy + UEFI) to pure UEFI mode in BIOS.

System Specs:

• CPU: AMD Ryzen 5 3600
• GPU: AMD Radeon RX 6600
• Motherboard: MSI B450 Mortar Max
• OS: Windows 11 Home (fresh clean install, official ISO)
• Disk: GPT (confirmed)
• TPM: 2.0 (ready and enabled)

Summary of the Problem:

My system is completely stable under BIOS default settings. I can use my PC normally, browse, and play games (e.g., PUBG) without any crashes or issues.

However, the moment I change BIOS settings to meet UEFI/Secure Boot requirements, the problem starts.

Changes made:

• Boot Mode: Legacy + UEFI → UEFI only
• CSM: Enabled → Disabled
• (Secure Boot attempted after this, but instability already appears even before enabling it)

After switching to UEFI:

• Browser starts crashing (“Aw Snap” errors)
• System becomes unstable
• Running sfc /scannow reports:
  “Windows Resource Protection found corrupt files but was unable to fix some of them”
• Issue repeats even after a fresh reinstall of Windows 11

What I have already done:

• Clean installed Windows 11 Home multiple times (official installer)
• Confirmed disk is GPT
• Confirmed TPM 2.0 is enabled and ready
• Installed latest AMD chipset drivers
• Installed latest GPU drivers
• Fully updated Windows
• Ran DISM:
  “No component store corruption detected”
• Ran SFC:
  clean when BIOS is in default settings
• Reverted BIOS to defaults → system becomes stable again

Key Observation:

• BIOS Default (CSM enabled / Legacy + UEFI) → stable
• Pure UEFI mode (CSM disabled) → instability + file corruption
• Issue is fully reproducible

Questions:

• Is this a known issue with B450 motherboards or Ryzen 3000 CPUs when using UEFI on Windows 11?
• Could this be related to memory training, fTPM, or firmware compatibility?
• Why would switching to UEFI mode cause system instability and file corruption on a clean install?
• Are there specific BIOS settings required to stabilize UEFI mode on this platform?

At this point, my system is only stable when using BIOS default settings, which prevents me from enabling Secure Boot (required by some applications like Valorant).

Any help or insight would be greatly appreciated.

Thank you!

Answer 1

Hi LUIGGI BANARES,

From your observations, the issue is not Windows itself but rather how the firmware and hardware interact when CSM is disabled. On some older B450 boards, disabling CSM can expose compatibility gaps in the UEFI implementation, especially with Ryzen 3000 CPUs. This can lead to memory training inconsistencies or fTPM measurement mismatches that BitLocker and Secure Boot interpret as corruption.

A few steps you can try: ensure you are running the latest BIOS from MSI, as many updates improve UEFI stability. Double‑check that your storage controller is set to AHCI mode and that all boot devices are properly recognized in UEFI. It may also help to clear the fTPM and re‑initialize it after switching to UEFI, so that Windows can establish a clean baseline. Some users have found that disabling “Fast Boot” in BIOS reduces instability in this scenario.

It’s not a broadly documented issue with Ryzen 3000, but rather a firmware maturity issue on older boards. Secure Boot itself should not cause corruption, but the transition from mixed CSM to pure UEFI can expose driver or firmware bugs. If instability persists even after BIOS updates, you may need to keep CSM enabled until MSI releases a firmware fix.

In short, update BIOS, reset fTPM, check storage mode, and disable Fast Boot to stabilize UEFI mode. I hope this gives you a clear path forward. If you find this answer helpful, please consider clicking Accept Answer so others can benefit too.

Jason.

Answer 2

Switching from CSM/Legacy to pure UEFI should not by itself cause file corruption on a healthy system. The behavior described points to a firmware/boot-path problem rather than a Windows 11–specific limitation of B450 or Ryzen 3000.

From the available information, the most relevant guidance is:

1. Check UEFI/CSM storage driver behavior

On some systems that support both legacy option ROMs and UEFI, the firmware can change which storage drivers are used depending on mode. If legacy option ROMs are prioritized or only support 32‑bit LBA, access to parts of the disk can be unreliable when using large disks or certain layouts. This can lead to boot or file access issues when the system is in a particular firmware mode.

The documented behavior is:

• Some UEFI implementations in “Class 2” mode (CSM + UEFI) may prefer traditional option ROMs that only support 32‑bit LBA.
• When partitions or files end up beyond the accessible range, boot or file access can fail after maintenance/servicing operations.

Recommended mitigations from this scenario that apply to this case:

• In firmware, prefer pure UEFI storage drivers instead of legacy option ROMs when CSM is disabled.
• If the firmware exposes a setting to choose between legacy option ROM and UEFI drivers for storage, explicitly select UEFI drivers.
• Ensure the boot and OS partitions are sized/placed so that their last logical block address is below the 2 TB boundary if using hardware/firmware that might still rely on 32‑bit LBA in some modes.

On a B450 board, this translates to:

• In BIOS/UEFI setup, look for options that control:
  • CSM / Legacy ROM usage per device (especially storage).
  • Storage boot option control (UEFI only vs Legacy/UEFI).
• Ensure storage is configured to use UEFI drivers only when CSM is disabled.

2. Verify UEFI boot path and recovery

If switching to UEFI has already led to corruption or unstable boot files, restoring the EFI boot files from within Windows can help once the system is bootable again (for example, after reverting to a stable configuration):

• From an elevated Command Prompt in a working Windows session:
  1. mountvol S: /s to mount the EFI System Partition.
  2. Optionally clean EFI boot files if instructed in a recovery scenario.
  3. Rebuild boot files with:
     • bcdboot %systemroot% /s S:

This process is used in Secure Boot/boot manager recovery scenarios to restore consistent EFI boot files and can be applied after firmware/boot-mode changes that destabilize the boot path.

3. Secure Boot and UEFI stability

To meet Secure Boot requirements on Windows 11:

• System must be in UEFI mode (not Legacy/CSM).
• Secure Boot must be enabled with valid keys.

If enabling UEFI mode alone causes instability:

• First stabilize UEFI boot without Secure Boot:
  • Disable CSM.
  • Ensure storage is using UEFI drivers.
  • Confirm Windows is installed in UEFI mode on a GPT disk.
• Once stable, enable Secure Boot:
  • Enter firmware settings and enable Secure Boot under Security/Boot/Authentication.
  • If Secure Boot fails or causes boot issues, reset Secure Boot keys to factory defaults and then re-enable.

If the system becomes unbootable or unstable after Secure Boot changes, the documented recovery path is:

• Turn off Secure Boot in UEFI.
• Reset Secure Boot keys to factory defaults (use “Reset” rather than “Clear” if both exist).
• Boot Windows and, if needed, restore EFI boot files using mountvol + bcdboot as above.
• Re-enable Secure Boot once Windows boots reliably.

4. When to involve the motherboard vendor

If instability and file corruption only occur in pure UEFI mode and not with CSM enabled, and the disk is GPT with a clean Windows 11 install, this strongly suggests a firmware-level issue:

• Check for the latest BIOS/UEFI update from MSI for the B450 Mortar Max.
• If already on the latest version, contact MSI support and describe:
  • Stable behavior with CSM/Legacy+UEFI.
  • Reproducible instability and SFC corruption when CSM is disabled and UEFI-only is used.
  • Disk is GPT and Windows 11 is clean-installed in UEFI mode.

The documented guidance for similar UEFI/boot issues is that OEMs may need to provide firmware updates or configuration options to ensure UEFI drivers are used correctly and that storage beyond certain limits is handled safely.

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References:

• A UEFI mode system cannot boot after maintenance or servicing activity
• How to manage the Windows Boot Manager revocations for Secure Boot changes associated with CVE-2023-24932
• Disabling Secure Boot