Steps to reproduce:

1) Download attached project and open in Unity
2) Build and run 'scn_Main' scene on a device
3) Log in with given credentials(check Edit field)
4) Click on the "matt" username
5) After thread loads press device's back button
6) Press device's back button again
7) Press 'Yes' after pop up appears
Note: after ~ 3 seconds application will crash
Fatal signal 11 (SIGSEGV), code 1, fault addr 0x8 in tid 2442 (UnityMain)

Reproduced with:
5.4.1p3, 5.4.2f1, 5.4.4f1

Not reproduced with:
5.4.0f1, 5.4.1p2

Regression started in: 5.4.1p3

Note: Check Edit field to see additional information

DUT:
Reproduced with:
Samsung Galaxy S 7 [SM-G930V], Qualcomm Snapdragon 820, OS version 6.0.1
Samsung Galaxy S 6 edge[SM-G925F], Exynos 7 Octa, OS version 6.0.1
Samsung Galaxy S 5 Neo[SM-G903F], Samsung Exynos 7 Octa, OS version 5.1.1

Not reproduced with:
Meizu MX5, MediaTek,OS version 5.0.1

------------------------------------------------
Fixed in 5.6.2p4, 5.5.3p3 and 5.4.5p2