Sony A7C ARWs with identical exposure render at different brightness in ACR 18.5.

Camera: Sony A7C (ILCE-7C)
Software: Adobe Camera Raw 18.5 / Lightroom Classic
File format: Sony ARW
Lens: Laowa 100mm Macro, manual aperture (f/5.6)

I noticed that consecutive photos taken in continuous shooting mode are sometimes rendered at dramatically different brightness levels by Adobe Camera Raw/Lightroom, even though the exposure settings are identical.

Example:

A7C05734.ARW — ISO 6400, 1/100 sec — rendered dark
A7C05735.ARW — ISO 6400, 1/100 sec — rendered much brighter

The aperture is fully manual on this lens, so it cannot change between frames.

The difference is NOT present when the same ARW files are opened in Sony Imaging Edge. The files appear essentially equally exposed there. The embedded/system previews also do not show the large exposure difference seen in Adobe.

I compared the RAW data and metadata and found a reproducible difference in Sony RAW SubIFD tag 0x7316:

A7C05734.ARW: 0x7316 = 128 (0x0080) → Adobe renders dark
A7C05735.ARW: 0x7316 = 65535 (0xFFFF) → Adobe renders bright

The same correlation occurs in another consecutive pair:

A7C05737.ARW: 0x7316 = 128 → dark
A7C05738.ARW: 0x7316 = 65535 → bright

To test causality, I made a copy of A7C05735.ARW and changed only the two-byte value of tag 0x7316 from 0xFFFF to 0x0080, without changing the RAW image data or rebuilding the ARW structure.

When this modified file is opened in Adobe Camera Raw, it changes from the bright rendering to the dark rendering, closely matching A7C05734.ARW.

Therefore, Adobe Camera Raw appears to use Sony SubIFD tag 0x7316 when determining the base rendering/exposure of this ARW file. The 0xFFFF value appears to cause substantially different brightness processing. Sony Imaging Edge does not exhibit this behavior.

All Adobe Develop settings are at defaults (Exposure 0.00, Highlights 0, Shadows 0, Whites 0, Blacks 0, Adobe Color profile), so the brightness difference occurs before user exposure adjustments.

Steps to reproduce:

1. Open the supplied original A7C05734.ARW and A7C05735.ARW in Camera Raw 18.5.
2. Observe the substantial brightness difference.
3. Open the same files in Sony Imaging Edge and observe that the large brightness difference is absent.
4. Open the supplied modified copy of A7C05735, where only tag 0x7316 has been changed from 0xFFFF to 0x0080.
5. Observe that Camera Raw now renders A7C05735 at approximately the same darker brightness as A7C05734.

I can provide all original ARW files and the two-byte-modified test file for reproduction.