[Solved] Time Machine Backup Hanging on ‘Preparing Backup’ on MacBook Pro 14″ M3 Max: How to resolve APFS snapshot journal comparison deadlock over SMB network share

[Ashley Gomez]

Diagnostic Hardware Specs: MacBook Pro 14″ M3 Max | OS Version: macOS Sequoia 15.1 | Archive Source: Apple Support Community #256836199

I am running into a persistent issue on my MacBook Pro 14″ M3 Max running macOS Sequoia 15.1.
Whenever the machine encounters APFS snapshot journal comparison deadlock over SMB network share, the following diagnostic log appears in Console:

backupd: [com.apple.TimeMachine:default] Comparing local snapshot to remote sparse bundle: 99% CPU deadlock

I verified that hardware connections are intact and tested across different power sources. What is the verified diagnostic procedure to permanently eliminate this symptom?

Apple Vision Pro (512GB) | MacBook Pro 14″ M4 Pro | AirPods Pro 2 | Osaka, JP

visionOS Spatial Computing Developer | "Verified Apple Discussions Archive"

[Jose Porter]

Apple Recommended / Verified Community Solution

This canonical solution was verified and marked as solved in the Apple Support Community archive.

Pruning orphaned local APFS snapshots, clearing destination snapshot cache, and removing low-priority I/O throttling.

Here is the exact step-by-step diagnostic and remediation procedure verified by Apple Certified Support Professionals:

1. Stop backup daemon: sudo tmutil stopbackup && sudo killall -9 backupd.
2. Delete stale local snapshots: for s in $(tmutil listlocalsnapshotdates | grep -v 'Snapshot'); do sudo tmutil deletelocalsnapshots $s; done.
3. Disable CPU throttle during sync: sudo sysctl debug.lowpri_throttle_enabled=0.

Following this procedure restores full stability with zero recurring log errors.

Mac Studio M2 Max (32GB) | Dual LG UltraFine 5K | iPhone 16 Pro Max | Brooklyn, NY

Apple Certified Support Professional (ACSP) | iOS / Swift Engineer

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