Sprites are cut off when using a custom alpha mask with a custom shader

Reproduction steps:
1. Open the attached “IN-112115_Sprites Cut Off Issue.zip“ project using Unity 6 (link in the internal comments)
2. Open the “SampleScene”
3. Enter Play mode and observe the Game view

Expected result: The jigsaw male connections (“Images” > “Giver.png” connections on “PuzzlePiece(Clone)” GameObjects) are rendered full and round
Actual result: The jigsaw male connections (“Images” > “Giver.png” connections on “PuzzlePiece(Clone)” GameObjects) are cut off

Reproducible with: 2021.2.0a1, 2021.3.55f1, 2022.3.65f1, 6000.0.56f1, 6000.2.1f1, 6000.3.0a5
Not reproducible with: 2020.3.48f1

Reproduced on: Windows 11 Pro (24H2)
Not reproduced on: No other environment tested

Notes:

• Reproducible in the Player
• The regression happened in the Unity 2021.1 stream, however, this stream is no longer supported for further regression testing and for considering it as a regression (the customer was trying to incrementally upgrade from Unity 2019 to Unity 6 when they discovered this issue in Unity 2021)
• Could not test in a new project (due to the unclear nature of the culprit for this issue)