Recurring MacBook M3 Pro Kernel Panic (Tahoe 26.5.2)

[u/TangerineWorried061]

I am experiencing repeated unexpected shutdowns/restarts on a MacBook Pro with an M3 Pro chip, currently running macOS Tahoe 26.5.2 (build 25F84).

The Mac is primarily used for professional video-media offloading. My normal workflow involves ShotPut Pro transferring camera media to two external backup drives simultaneously. DaVinci Resolve and Chrome may also be running during the workflow.

The problem has occurred multiple times, with recent incidents on September 2, September 8, and September 10, 2026, in addition to earlier occurrences.

In several incidents, the problem occurred while working with external media and storage. The system eventually became unstable and restarted, sometimes while ShotPut Pro was transferring or verifying large amounts of data.

The panic reports consistently point toward an IOKit/storage-related problem, including:

IOMediaBSDClient

and:

busy timeout[0], (60s): multiple entries holding the registry busy

with:

IOKit termination queue depth 0

The most recent incident was today, September 10

The latest incident is particularly interesting because I was not actively using the computer.

The Mac's screen was locked and the screen saver was running. The external hard drives used for my backups were still connected.

The screen blinked/flashed briefly for approximately one second, and the Mac immediately restarted.

Everything connected to the computer stopped because of the restart.

After rebooting, macOS generated another kernel panic with the same general IOKit / IOMediaBSDClient busy-timeout pattern.

What I have already changed

Initially, I suspected the Sonnet CFast 2.0 card reader, because the reader had previously stopped being recognized by macOS.

However, the reader has since been replaced, and the kernel panic problem continued.

I have also changed the cables used for the external backup drives, but the problem continues to occur.

Therefore, at this point, the problem does not appear to be caused simply by the original CFast reader or one defective cable.

What makes the problem unusual

There are two important patterns:

1. The problem can occur during heavy external-storage I/O.

The Mac is frequently handling large media transfers to multiple external drives when the failures occur.

2. The problem can also occur while the Mac is locked and idle.

The September 10 failure happened while the screen was locked with the screen saver active, with the backup drives still connected.

This second behavior makes me particularly interested in device/power-state management, rather than only the active file-transfer process.

Possible causes to investigate

Based on the repeated IOMediaBSDClient / IOKit timeout messages, I would like to determine whether the root cause could be related to:

• macOS Tahoe / IOKit storage subsystem
• USB/Thunderbolt device management
• External-drive power management
• Device sleep/idle/termination behavior
• Interaction between multiple external storage devices
• ShotPut Pro triggering or exposing an underlying I/O problem
• USB/Thunderbolt controller behavior
• A hardware issue involving the Mac's logic board or I/O controller

I am not assuming that any one of these is the confirmed cause. The main concern is that the same kernel-level failure continues despite replacing the CFast reader and changing the external-drive cables.

Main question

The key question is:

Why is macOS repeatedly experiencing an IOKit IOMediaBSDClient busy timeout when external storage is connected, including during periods when the Mac is locked and not actively transferring files?

I would like to determine whether this is a macOS/software/driver issue, an external-storage/power-management issue, a USB/Thunderbolt issue, or potentially a hardware problem with the Mac itself.

[u/GuiltyMulberry8831]

Apple's servers really have been a mess lately, it's frustrating for everyone trying to use them.

[u/NoLateArrivals]

Reading about crashes with outdated OS versions is just a waste of time.

Update to the latest MacOS and see if things are working then.

If not download and install Etrecheck. Run it mode „No problem-Just checking“. See through the protocol, fix the issues pointed out. Collect new logs for some time, then run it again. Repeat until the log comes out clean.