To reproduce:
1. Open attached project;
2. Open "TheScene" scene;
3. In hierarchy, choose Camera Root > Main Camera and change Max Recursive Depth to 1 or 2 (In Portal System script);
4. Enter playmode;
5. Exit playmode;
6. Change Max Recursive Depth to more than 2;
7. Repeat steps 4 and 5;
8. Observe crash.

Expected result: no crash.
Actual result: when Max Recursive Depth is more than 2, Editor crashes when leaving playmode.

Reproduced on versions: 5.4.1f1
Not reproduced on versions: 5.3.8f1, 5.4.1p1, 5.5.2p4, 5.6.0f2.