Bakes a colored geometric artifact into exported JPEGs from unedited iPhone 15 Pro DNG files (Lightroom Classic 15.5 / Camera Raw 18.5)

Product/Version: Lightroom Classic 15.5, Adobe Camera Raw 18.5 (August 2026 release)
OS: macOS
Camera/File type: DNG (ProRAW), iPhone 15 Pro back triple camera 6.765mm f/1.78

Description:
Certain unedited DNG photos show a small rectangular geometric artifact (jagged blue/cyan/green diagonal streaks fading to white) consistently positioned in the same spot on the image. This artifact appears in:

• macOS Finder preview (especially on window resize)
• Lightroom Classic Library grid and Develop module
• The final exported JPEG — the artifact is baked into the output file, not just the on-screen preview

Out of 964 photos in the catalog, 13 are affected so far, all unedited DNG files (no Develop adjustments applied), each with the artifact in a different location and size.

Steps to reproduce:

1. Open a catalog/folder containing unedited iPhone 15 Pro ProRAW DNG files.
2. Identify an affected photo (artifact visible in Finder preview, Library grid, or Develop module).
3. Export the photo to JPEG.
4. Open the exported JPEG — the same geometric artifact is present in the output file, at the same position seen in the preview.

What I've tried:

• Disabling GPU acceleration in Lightroom (Preferences > Performance > Use Graphics Processor: Off) — no change.
• This did not occur before the recent update — same photos, same catalog, previously displayed and exported correctly.
• Confirmed the artifact is reproducible and consistent across Finder, Lightroom, Camera Raw, and the final exported JPEG — not a transient rendering glitch only.

Additional notes:
Attached: Finder preview screenshot, Finder preview after window resize screenshot, Lightroom/Camera Raw Develop view screenshot, and the exported JPEG screenshot showing the same artifact baked in, all for file IMG_1098_20260413.DNG (4284x5712, iPhone 15 Pro).