AI Denoise fails with "An unexpected error occurred while processing" on every RAW file in Lightroom Classic 15.3.1 on macOS 26.5.1 (M1 Max, 64 GB RAM). Reinstalling Lightroom did not resolve the issue.

Lightroom Classic version: 15.3.1

Operating System: macOS 26.5.1

Computer: MacBook Pro M1 Max, 64 GB RAM

Cameras affected:

• Canon R5 Mark II

• Canon R6 Mark II

Description:

AI Denoise suddenly stopped working during an editing session. It had been working earlier the same day and then began failing on every RAW file.

The issue affects RAW files from both Canon cameras and occurs across different folders and catalogs.

When I select Photo → Enhance → Denoise → Enhance, Lightroom either displays:

"An unexpected error occurred while processing."

or no Enhanced DNG is created.

Troubleshooting already completed:

• Restarted Mac.

• Reinstalled Lightroom Classic.

• Cleared Camera Raw cache.

• Verified over 600 GB of free disk space.

• Tested multiple RAW files from different folders.

• Tested files from two different cameras.

• Catalog and RAW files are on an external drive.

• Lightroom edits, exports, and all other functions work normally.

• AI Denoise is the only feature that consistently fails.

This appears to be a regression because Denoise was working earlier in the same editing session before it suddenly stopped.