Lightroom Classic 15.0 (Camera Raw 18.0) fails to display Library previews for Leica Q2 Monochrome

Summary

After updating to Lightroom Classic 15.0 (Camera Raw 18.0), the Library module no longer displays thumbnails or Loupe previews for monochrome DNG files from the Leica Q2 Monochrom.

The images display and edit correctly in the Develop module, but the Library grid and Loupe views remain blank (gray boxes).

This issue did not exist in previous versions (Lightroom Classic 12.5 and earlier).

Affected versions

• Lightroom Classic 15.0

• Adobe Camera Raw 18.0

• Catalogs migrated from earlier versions (which rendered fine)

System details

• MacBook Pro (Apple M2 Max)

• macOS: [specify version, e.g., Sonoma 15.x / Sequoia 15.x]

• GPU acceleration: tested both On and Off

• Original DNG files stored on external APFS SSD (same issue when stored on internal drive)

Camera / File type

• Leica Q2 Monochrom

• Native monochrome DNG (single luminance channel)

• Occurs with both newly imported and previously cataloged files

Steps to reproduce

1. Open Lightroom Classic 15.0 (new or existing catalog).

2. Import Leica Q2 Monochrom DNG files (Add, Copy, or Move—makes no difference).

3. In Library module, switch to Grid or Loupe view.

4. All thumbnails and previews appear gray (no image rendered).

5. Switch to Develop module — image displays correctly and is fully editable.

Expected behavior

• Library thumbnails and previews should render correctly, as they did in LrC 12.5 and prior.

Actual behavior

• Library displays blank (gray) placeholders.

• Previews and Smart Previews (.lrprev / Smart Previews.lrdata) are generated but not rendered.

• Develop module renders the DNG correctly.

Tests performed (no success)

• Rebuilt Standard, 1:1, and Smart previews.

• Deleted and regenerated Previews.lrdata and Smart Previews.lrdata.

• Toggled GPU acceleration, HDR in Library, and preview cache sizes.

• Cleared Camera Raw cache and preview cache.

• Converted files again with Adobe DNG Converter (with embedded previews).

• Same behavior whether originals are on internal SSD or external APFS volume.

• Works perfectly when rolling back to LrC 12.5 (Sept 2023).

Technical hypothesis

The new RGB-based preview engine introduced in recent Camera Raw versions (17–18) appears to require three color channels and fails to render monochrome-only DNGs.

The Develop module still works because it uses the full Camera Raw pipeline, which correctly interprets single-channel luminance data.

Workarounds

• None reliable in 15.0.

• Reverting to Lightroom Classic 12.5 restores normal behavior.

• Using “Embedded & Sidecar Previews” (deprecated setting) used to work but is no longer available in v15.0.

• Users can still edit in Develop but cannot browse or cull images efficiently in Library.

Attachments recommended

• 2–3 Leica Q2 Monochrom DNG samples

• Screenshots: Library (blank thumbnails) and Develop (image visible)

• System Info (from Help → System Info)

• Catalog info (optional)

Request

• Confirmation that this bug is recognized.

• Status update on the fix for Lightroom Classic 15.x / Camera Raw 18.x.

• Temporary workaround or rollback recommendation until Adobe releases a patch.