Reproduction steps:
1. Create a new Universal 2D project
2. Open Tile Palette window (Window > 2D > Tile Palette)
3. Create New Tilemap > From Tile Palette
4. Create a 2D Sprite, drag it into the Tile Palette window (Create > 2D > Sprite)
5. Press “Tile Palette Brush Pick Overlay” button
6. Press “Save” button in Tile Palette Brush Pick Overlay to add a new saved Pick
7. Observe the newly created brush pick

Actual result: Rectangles are seen instead of the icons
Expected result: Icons are visible

Reproducible with: 6000.1.0b2, 6000.2.0a1, 6000.3.0a1, 6000.3.0b2
Not reproducible with: 6000.0.58f1, 6000.1.0b1, 6000.2.5f1
Couldn’t reproduce with: 2021.3.56f1, 2022.3.66f1 (No “Tile Palette Brush Pick Overlay” button)

Reproduced on: Windows 11, macOS Sequoia 15.6 (Intel)

Note:
* Issue stops reproducing after adding another Pick
* Issue reproduces inconsistently on 6000.1.0b2-6000.1.0b3