Reproduction Steps:
1- Open the reproduction project.
2- Open scene "Crash.unity".
3- Enter and exit play mode repeatedly and quickly. (e.g. once in every 2 seconds)

Expected Result: Editor goes in and out of the play mode without any problems.
Observed Result: Editor crashes, sometimes after the first try, sometimes after 5-6 tries.

Reproducible: 2017.1.0a3, 2017.1.0a2, 5.6.0b11
Not Reproducible: 2017.1.0a1, 5.6.0b10, 5.5.2f1
Regression Introduced with: 2017.1.0a2, 5.6.0b11

Notes:
-If you remove the Animator component on game object Canvas > LaBomb, or break prefab instance, crash does not occur.
-Crash occurs in "mono_add_process_object".