Steps to reproduce:

1) Download repro project from OwnCloud and open in Unity
2) Make sure that Install Location in Player settings is set to 'Prefer External'
3) Make sure that device under test has external memory(SD card)
4) Build and Run 'TestScene' on a device
5) Press on 'Add file' button
6) Choose a location of SD card and press on 'Select' button(bottom right)
7) Press on new generated button which should display created file's path
Pop up 'lolol' should be displayed on the screen(expected)
8) Close the app and restart device
9) Open application again and click on file's path button
Permission to read this file will be denied

Expected result: Permission to read files from external storage should be allowed after device was restarted
Actual result: Permission to read files from external storage is denied after device was restarted

Reproduced with:
5.5.4p1, 5.6.2f1, 2017.1.0b10, 2017.2.0a4

Devices under test:
Verizon SM G930V*, OS:6.0.1, CPU:arm64-v8a, GPU:Adreno (TM) 530, Build:Verizon/heroqltevzw/heroqltevzw:6.0.1/MMB29M/G930VVRU2APG3:user/release-keys

Samsung SM G903F*, OS:6.0.1, CPU:armeabi-v7a, GPU:Mali-T720, Build:samsung/s5neoltexx/s5neolte:6.0.1/MMB29K/G903FXXU1BPF4:user/release-keys

Note: Works fine if application was installed in the Internal storage