I have recently updated my Moto G3 and inserted a microSD card, formatting it for use as internal storage. I have used Solid Explorer app for file management before and I was able to manage internal & external storage separately before the OS update. Now the app cannot access the internal memory. It can access the SD card as internal storage only.When I connect my phone to my PC (Windows 8), it can also access SD card as internal storage only. Why is this happening? Is there a file management app which can access the real internal storage?
This is intentional by the Android system. When you format a microSD card to be used as internal storage, 2 things basically happen:
The microSD card becomes locked-in to the device (as it is specifically encrypted for the device)
The real internal storage (eMMC) becomes invisible to non-root and non-system privileged users. You could still technically access it by rooting your device and using a Root Explorer app, but it's not properly mounted, but your PC still con't be able to detect the real internal storage over USB MTP.
Notice that the space is not increased by the size of the sdcard, but to the size of the sdcard. You’re basically swapping out your internal storage (which is typically eMMC, which is fairly quick), with your sdcard (which is typically slower than the built-in storage chip). You’ll be trading speed for capacity.
You could use ADB as root to push/pull data, but doing that via the command line is cumbersome, and even using a GUI ADB client for this purpose seems like a waste of time.
As to what you can do, you can reformat the microSD to be used as portable storage, and then you will be able to use it as you did in previous versions of Android (but you won't be able to move apps to it).
You can change it back by heading to Settings>Storage & USB, then selecting the card, hitting the top right menu and then select ‘Format as portable’.
Source: How does the "Format as internal storage" feature work in Android 6.0+? and links therein.