1. Download attached project "Sand_6_v2"
2. Open scene "Scene 1"
3. Notice that it contains a lot of game objects. That's the same game object cloned multiple times and purpose of this is to ease repro as it's all about timing
4. Open build settings, press build and run, enter scene name and tap enter
5. Quickly cancel build before new blank scene gets opened (as per usual build process)
6. Expand any GameObject and notice that all mesh filters are stuck with combined meshes

Reproducible with: 5.5.0f3, 5.5.4p2, 5.6.0f2, 5.6.2p4
Not reproducible with - 2017.1.0a3

Notes:
1. Probably not the only way to reproduce the bug, other users are experiencing this issue after downgrading, light baking or etc
2. Can't reproduce the issue with 5.4 version of Unity, since the project gets corrupted and couldn't cause the issue with my own project

Fixed in 5.6.3p2