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Gerzson Réti
Known Participant
October 7, 2026

Lightroom Classic becomes severely unresponsive and exceeds 1000% CPU when Cloud Sync runs during bulk Develop Copy/Paste operations on Apple Silicon

  • October 7, 2026
  • 2 replies
  • 35 views

I am experiencing a reproducible and severe performance/unresponsiveness issue in Lightroom Classic 15.6 on Apple Silicon.

Environment:
- Lightroom Classic 15.6
- Apple Silicon Mac
- M2 Max
- 64 GB unified memory
- Lightroom Classic running natively as ARM64
- Large Lightroom catalog

Problem:
Lightroom Classic becomes severely unresponsive when Cloud Sync is running at the same time as a large number of Develop Copy/Paste operations.

The issue is highly reproducible.

Reproduction steps:
1. Open Lightroom Classic.
2. Start syncing approximately 450 photos to Lightroom Cloud.
3. While the sync is running, perform a large number of Develop Copy/Paste operations on photos in the catalog.
4. Continue performing these operations while Cloud Sync is active.
5. Lightroom Classic CPU usage increases dramatically, reaching several hundred percent and, in the latest reproduction, exceeding 1000%.
6. At the same time, Lightroom Classic becomes extremely sluggish and stops responding normally to user input.
7. Operations that should be immediate can take many seconds, and in previous occurrences Lightroom Classic has become so unresponsive that I had to force quit the application.

Important observations:
This does not appear to be caused by lack of system resources.

During the reproduction:
- macOS still had substantial CPU capacity available.
- Memory pressure remained green.
- There was no significant swap usage.
- Current disk I/O was very low.
- Network activity was relatively low.
- The high CPU usage was concentrated in Lightroom Classic itself.

I captured an Activity Monitor Sample while the issue was actively occurring.

The Sample shows substantial activity inside Lightroom Classic's internal processing, including repeated AgKernel / Lua / AgSubstrate / WichitaFoundation call chains in the MainServer thread.

The Sample also shows active CameraRaw processing and a GPUImageView background queue involving CameraRaw and Apple Metal/AGX GPU processing.

Lightroom's sync infrastructure is also present in the captured state, including SyncServer and the com.adobe.ngl-RecurringSync thread. The RecurringSync thread itself was waiting on a condition variable at the exact moment of the sample, so I am not claiming that this particular thread alone is responsible for the CPU usage.

The important point is that the combination of Cloud Sync + bulk Develop Copy/Paste produces a state in which Lightroom Classic can exceed 1000% CPU usage and becomes severely unresponsive, despite the Mac itself still having available system resources.

Expected behavior:
Lightroom Classic should remain reasonably responsive while Cloud Sync and background processing are running. Background synchronization and Develop operations should not make the application effectively unusable.

Actual behavior:
When these operations overlap, Lightroom Classic can consume more than 1000% CPU and become severely unresponsive. The problem has occurred repeatedly over a long period of time and has persisted across multiple Lightroom Classic versions and Apple Silicon Macs.

I have submitted Adobe crash reports for similar Lightroom Classic hangs and forced quits over the years, but the underlying performance/unresponsiveness issue has persisted.

I can provide the Activity Monitor Sample and additional screenshots or diagnostic information if required.

    2 replies

    Claire H.
    Community Manager
    Claire H.Community Manager
    Community Manager
    October 7, 2026

    Hi @Gerzson Réti, Thank you for the detailed report. High CPU usage when cloud sync runs during bulk development. Copy/paste is a known contention area where sync and Development rendering compete for the same resources, which hits especially hard on Apple Silicon during large batch operations.

    Immediate workarounds:

    1. Pause Sync before bulk edits: Click the cloud icon (upper-right) → Pause Syncing. Resume once your batch finishes.

    2. Batch smaller: Try groups of 50–100 images instead of hundreds at once.

    To help us investigate further, please share:

    • Help > System Info, copying and pasting it into a text file, and attaching it here

    • Activity Monitor screenshot while reproducing the issue

    • Your approximate catalog size and how many images are synced to the cloud

    We're actively tracking CPU behavior during sync operations, and your report helps us investigate this issue. Thank you! ^CH

    Gerzson RétiAuthor
    Known Participant
    October 8, 2026

    Hi Claire,

    Thank you. I can provide the requested information.

    There is one important detail that may be particularly relevant to the investigation: the issue does not depend on the size of the catalog or the number of photos synced to the cloud.

    I have reproduced the same behavior under very different catalog sizes and cloud-sync counts.

    Previous catalog: approximately 800,000 photos. The same issue occurred there.

    I then took that catalog offline and removed its cloud-synced content. I subsequently created a completely new Lightroom Classic catalog from scratch.

    In the new catalog, the same problem was already reproducible after the first photo shoot, with only approximately 350 photos in the catalog.

    The problem also occurred on an M4 MacBook Air, not only on my M2 Max.

    I have also observed the same behavior when only a small number of photos existed in Lightroom Cloud, as well as later when the cloud contained tens of thousands of photos.

    My current catalog contains approximately 107,000 photos, of which approximately 27,500 are currently synced to Lightroom Cloud.

    Therefore, based on my testing, I do not believe that the catalog size or the total number of cloud-synced photos is the primary cause.

    The common factor appears to be the interaction between active Cloud Sync and Develop operations, particularly repeated Copy/Paste operations, regardless of catalog size or total cloud content.

    This is also why simply reducing the batch size may reduce the severity, but it does not eliminate the underlying issue. I have reproduced it with a very small, newly created catalog as well.

     

    I would also like to emphasize that this is not a new issue. I have been experiencing Lightroom Classic freezes and severe unresponsiveness for several years, including a very large number of freezes and forced quits. I have submitted Adobe crash reports on these occasions whenever prompted. Despite repeatedly reporting these incidents to Adobe over the years, the underlying problem has persisted.

    This is one of the reasons I am providing the detailed reproduction steps and Activity Monitor Sample now. I would like to help determine whether these long-standing freezes are related to the same Sync/Development resource contention that you mentioned.

     

    I will attach the System Info and the Activity Monitor information you requested.

    Best regards,
    Gerzson Réti

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