On a Mac mini M4 Pro running macOS Tahoe 26.6, Lightroom Classic 15.3 through 15.5 consistently hangs when generating Standard Previews.

On a Mac mini M4 Pro running macOS Tahoe 26.6, Lightroom Classic 15.3 through 15.5 consistently hangs when generating Standard Previews.

Environment

• Hardware: Mac mini M4 Pro

• Operating System: macOS Tahoe 26.6

• Lightroom Classic versions tested:

  • ✅ 15.2.1 – Works correctly

  • ❌ 15.3 – Hangs

  • ❌ 15.3.1 – Hangs

  • ❌ 15.4.1 – Hangs

  • ❌ 15.5 – Hangs

Issue

When selecting photos and choosing Library → Previews → Build Standard Previews, Lightroom starts generating previews but then freezes indefinitely. The progress may stop at different points (for example 4/4, 5/68, or 100%), but it never completes.

During the freeze:

• Lightroom remains responsive, but the preview generation never finishes.

• CPU usage stays around 0–5%, indicating that the process is idle rather than actively rendering.

Troubleshooting Performed

The following steps did not resolve the issue:

• Disabled GPU acceleration.

• Deleted the preview cache (Previews.lrdata).

• Optimized the catalog.

• Tested multiple catalogs, including backups from several months ago.

• Tested multiple image folders.

A newly created catalog works correctly. However, the same original catalog and image files also work perfectly in Lightroom Classic 15.2.1, confirming that the issue was introduced starting with version 15.3.

This strongly suggests a regression in Lightroom Classic affecting Standard Preview generation.