[INSIDER BETA] Critical EFI/BCD corruption

Hello,

I’m dealing with a critical boot failure after a Windows Insider Beta update on Windows, and I’ve reached a point where even low-level recovery and clean installation fail.

Initial failure

• BSOD after update (error 0x80070003)
• System now fails immediately after BIOS (UEFI)
• Automatic Repair loop with no resolution

Environment

• UEFI firmware (CSM disabled)
• GPT partitioning
• Multi-disk setup:
  • 1 × 2TB (data disk)
  • 2 × 1TB (one was system disk ~930GB)
  • 1 × 115GB
• Windows originally installed on 1TB disk

Diagnostics

• Windows installation still present and accessible (D:\Windows)
• System32 intact and readable
• Disk health OK (no filesystem corruption detected)
• SrtTrail.txt shows:
  • All tests passing (0x0)
  • Failure specifically at Boot Manager stage

Boot repair attempts

Executed from WinRE:

• bootrec /fixmbr → OK
• bootrec /fixboot → Access denied
• bootrec /scanos → Detects 2 Windows installations
• bootrec /rebuildbcd → Partial/inconsistent rebuild
• bcdboot D:\Windows (multiple variants):
  • /s S:
  • /f UEFI /f ALL
  • without /f

Consistent errors:

• “Failed to validate boot manager checksum”
• “Failure when attempting to copy boot files”
• EFI partition access issues (locked / access denied)

EFI manipulation

• Identified multiple EFI partitions across disks
• Mounted correct FAT32 EFI partition (~100MB)
• Fully wiped and recreated EFI structure:
  • deleted EFI folder
  • reformatted FAT32
• Reattempted bcdboot → same failures

Clean install attempts

• Booted from Windows installation media
• Used diskpart:
  • clean
  • convert gpt
• Disk shows as unallocated

Installation errors:

• “Windows could not update the computer’s boot configuration”
• “An error occurred while selecting this partition” (on all partitions)

Observations

• Disk is writable (partitioning works)
• Filesystem operations succeed
• Boot-related writes consistently fail
• Behavior persists even after full disk wipe

Hypothesis

This appears to be a low-level inconsistency involving:

• EFI Boot Manager corruption (bootmgfw.efi / BCD integrity)
• UEFI NVRAM boot entries corruption or desync
• Possible firmware-level refusal to accept new boot entries
• Potential interaction with Insider Beta update affecting boot validation

Request for guidance

Looking for advanced guidance on:

• Forcing a complete reset/rebuild of EFI boot entries at firmware level
• Clearing or rebuilding UEFI NVRAM boot configuration
• Bypassing boot manager checksum validation failure
• Any known Insider-related issues causing boot installation failure even after disk wipe

At this stage:

• Standard recovery tools fail
• bcdboot fails
• clean install fails

Any low-level recovery method or firmware-level reset procedure would be greatly appreciated.

Thanks in advance.