Ist MBR→GPT-Konvertierung mit MBR2GPT der Grund für Updatefehler?

Is MBR→GPT conversion with MBR2GPT the cause of update errors?

Description:
I performed MBR to GPT conversion on five Windows 11 Pro PCs.
- On two systems with MBR to GPT (desktop PC and notebook), the update KB5070773 (build 26200.6901) resulted in error 0x800f0922, despite an increased ESP and a rewritten BCD.
- On three systems using a different known partition assistant for MBR to GPT conversion, the update proceeded without any issues.
- All systems are on version 25H2, with identical hardware and update configurations.
I suspect that MBR to GPT leaves a subtle inconsistency in the ESP or BCD structure, which leads to rollbacks with sensitive patches like KB5070773.

- The same problem and the same situation now also exist with .NET Framework Preview Update (KB5067931) and Preview Update (KB5067036) (26200.7019)

My affected cases might be more than just coincidence. It could indicate a possible systematic correlation between error 0x800f0922 and the type of MBR→GPT conversion.

Hypothesis: MBR2GPT generates "technically valid, but minimalist" ESPs.

Differences between the tools:

Tool, behavior during ESP creation, BCD/Bootloader, special features:

MBR2GPT (Microsoft): Creates a minimal ESP (100 MB) without additional buffers. Uses bcdboot, but without full validation. No GUI, no manual control.

Another well-known partition assistant: Creates larger ESPs (e.g., 300–500 MB). Often performs automatic BCD repair. GUI-guided migration, more redundancy.

Possible technical causes:

• MBR2GPT generates ESPs that are formally correct, but:

• Too small for later feature updates (originally 100 MB)
• Not correctly integrated into the firmware (missing efisys.bin structure)
• BCD store not fully synchronized

• Another well-known partition assistant, however, creates ESPs using:

• larger buffer
• more complete boat structure
• automatic BCD repair

My two affected systems out of my five systems in total:

• Both were converted using MBR2GPT (unlike my three other unaffected partitions, which were converted using a different well-known partition assistant).
• Both originally had 100 MB ESP.
• Both show error 0x800f0922 during cumulative updates after 25H2 (and previously after 24H2).
• Both have since been manually corrected (ESP enlarged, BCD rewritten)
• And yet the error remains.

This suggests that MBR2GPT leaves a subtle, persistent inconsistency that is not completely eliminated even by later fixes — at least not for KB5070773 (and KB5066835), which appears to be particularly sensitive to boot environments.

Possible deeper causes (speculation, but plausible):

• UEFI firmware does not recognize ESP as "fully trusted"
• The BCD store contains GUIDs or paths that originate from the MBR era.
• Secure Boot or Boot Manager denies update activation even though the system is running
• The update installer checks ESP/BCD for specific markers that are missing in MBR2GPT.

Conclusion:

If this connection is true, it would be highly relevant, as it would affect Microsoft's own tools. It's quite possible that MBR2GPT-converted systems have a silent vulnerability to certain update errors that only become apparent with sensitive patches like KB5070773 (and KB5066835).