Tiled Gallery: mosaic layout collapses to a single tile when images are uploaded directly into the block

### Impacted plugin

Jetpack

### Quick summary

Hi,

I've run into a reproducible issue with the Tiled Gallery block where the mosaic layout doesn't render if the images are uploaded at the moment the block is created.

**What happens:** I insert a Tiled Gallery block and upload several images to it directly from my computer. Once the upload finishes, the block shows a single full-width tile instead of the mosaic layout, and that one image is displayed at poor quality. The block reports the gallery as containing only one image. The same broken layout appears in the post preview, so it isn't limited to the editor view.

**What fixes it:** If I delete the block and insert a new Tiled Gallery block using the same images from the media library, everything renders correctly straight away — proper mosaic layout, all images, correct quality. Nothing else changes between the two attempts.

**Expected:** a mosaic layout containing all uploaded images.
**Actual:** one full-width tile, low quality, and the gallery is treated as having a single image.

Environment: WordPress 7.1, Jetpack 16.1.2, classic theme (Authentic 8.0.0 by CodeSupply), Gutenberg plugin not active, Jetpack connected with Image CDN working — images do get served from the Jetpack CDN once the gallery renders correctly.

(Artificial intelligence helped in writing the error message and phrasing it accurately.)

Thanks,
Csaba

### Steps to reproduce

On WordPress 7.1 with Jetpack 16.1.3, create a new post.
Insert a Tiled Gallery block and choose the Tiled mosaic style.
Upload four or more images to the block directly from your computer, rather than picking existing ones from the media library.
Wait for the uploads to complete and look at the block.

### Site owner impact

Fewer than 20% of the total website/platform users

### Severity

Moderate

### What other impact(s) does this issue have?

_No response_

### If a workaround is available, please outline it here.

_No response_

### Platform (Simple and/or Atomic)

_No response_