Reproduction steps:
1. Open attached project (Grocery.zip);
2. Go to Gameplay Balance Settings -> Level_003 and select Wave_Level_03_01 asset file;
3. Then go to the Receivers -> Cyans -> Cyan-Reds and drag Receiver_Cyan1 into Receivers/Element 0/Receivers field in the Inspector;
4. Observe the crash.

Also here is a link to the reproduction video:
https://drive.google.com/open?id=0B6Tp6DGuHBIlbE11MHViemNMeFU

Reproduce on: 5.6.0b2 version;
Not reproduced on: 5.5.0f3 version.

Note: the crash is reproducible only on the Windows 10.