To reproduce:
1. Download Space Shooter project from the Asset Store to 2018.2;
2. Upgrade the project to 2018.3.0a7;
3. Enter playmode.

Expected result: project was ugraded successfully, all collisions work: when Player collides with Asteroid (or is shot by Enemy’s bullet), the game is over, player dies
Actual results: player game object doesn’t collide with Asteroids or Enemy bullets (it dies only after touching the enemy)

Reproduced with: 2018.3.0a7
Not reproduced with: 2018.3.0a6

Regression introduced in 2018.3.0a7 where Nested Prefabs when merged into Trunk.

Fixed in: 2018.3.0b1