So, just as question states. Android device monitor is not showing anything in the File Explorer view. This is only occuring on Virtual Devices running Android API Level 24
I had this problem with Api 27 (Oreo). I tried to create emulator with Lollipop but same as with Oreo. Device monitor was empty.
After restarting computer everything was normal. This is solution for many problems that comes with Android Studio. First check this, than everything else.