How to reproduce:
1. Open the attached “collisions.zip” project
2. Open “Particle collision test” Scene
3. Open Project Settings > Tags and Layer and set “User Layer 6” to “test”
4. In the Hierarchy window, select “GameObject” GameObject
5. In the Inspector window, open the “Collision” tab of the “Particle System” Component
6. Set “test” in “Collides With” field
7. Select “GameObject” GameObject that’s inside “Cube” GameObject
8. In the Inspector window, change “Layer” to “test”
9. Select “Cube” GameObject and remove the “Rigidbody” Component
10. Enter Play Mode and observe the Console window

Expected result: “Other object: Collision object, other layer: test” is logged
Actual result: “Other object: Cube, other layer: Default” is logged

Reproducible with: 2021.3.34f1, 2022.3.17f1, 2023.2.6f1, 2023.3.0b3

Reproduced on: macOS 13.6.3 (Intel)
Not reproducible on: No other environment tested

Note: not reproducible without a “Rigidbody” Component