External USB-C NVMe enclosure mounts read-only as APFS on macOS 12.6 after system update

Environment

Intel MacBook Pro running macOS 12.6, external NVMe SSD in a USB-C NVMe-to-USB enclosure formatted APFS, enclosure firmware unknown, enclosure connects via a hub to the Mac; drive contains user documents and a live project workspace.

Symptoms

After installing macOS 12.6 the external drive mounts normally but Finder shows files as read-only; attempts to create or modify files fail with 'The operation can’t be completed. (com.apple.DiskManagement error -69845.)'; terminal 'touch' returns 'Read-only file system'.

Observations

diskutil info /Volumes/External shows 'Read-Only: Yes' and 'Filesystem Personality: APFS'; system log (Console.app) shows kernel messages indicating the device was mounted read-only due to I/O errors and a 'SCSI read-only condition' returned by the USB bridge; running First Aid in Disk Utility reports 'The volume appears to be OK' but cannot change mount options; drive works as read-write on a Linux machine when connected via a different external enclosure.

Already attempted

Ran Disk Utility First Aid, unmounted and remounted with sudo diskutil mount readWrite; tried mount -uw /Volumes/External but the system refused; swapped the USB-C cable and bypassed the hub; connected the same NVMe in a different enclosure where it mounted read-write on Linux; ensured no SIP changes were made and rebooted macOS into Recovery and checked security settings.

Question

How can I regain safe read-write access to the APFS volume on macOS without losing data, and how do I determine whether the issue is the USB-SATA/NVMe bridge firmware, macOS APFS change, or a compatibility regression introduced by the 12.6 update?

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AI DIAGNOSTICS

Incident analysis

Updated 1w ago• Trouble ID

Most likely causes

USB-to-NVMe bridge firmware incompatibility with macOS 12.6 causing the device to advertise read-only 85%

macOS 12.6 changed handling of certain USB error codes and forces read-only mounts on non-compliant bridges 80%

Power delivery or hub-related issues causing the enclosure to fail write initialization 10%

Summary

The enclosure firmware (USB-SATA/NVMe bridge) is returning a read-only condition to macOS, likely because macOS 12.6 interprets a returned SCSI/USB status as requiring a read-only mount. The fact that the same NVMe is writable in a different enclosure and that diskutil reports I/O-level flags suggests hardware/firmware incompatibility rather than APFS corruption. Other possible contributors include tightened APFS mount semantics in macOS 12.6, changes in USB power management, or a transient file-system flag set by previous unclean disconnection.

Suggested Fixes

Diagnostic step 1

Do not attempt a filesystem repair that writes to the volume until you have a block-level copy; create a byte-for-byte backup using dd or a cloning tool to another drive on Linux where the device mounts read-write.

Diagnostic step 2

Test the NVMe in a known-good enclosure that previously worked with macOS to confirm enclosure vs. drive behavior (reversible swap test).

Diagnostic step 3

Check for firmware updates for the USB-C enclosure and, if available, apply them following vendor instructions; if vendor firmware is unsigned, avoid risky firmware flashes.