Android 6.0 Marshmallow adoptable storage - Why is it still using internal storage? I have a 32GB MicroSD card adopted as internal storage on my Moto X Play (XT1563), and I've noticed that some apps don't completely move over to External Storage (specifically .obb files), despite what this new feature in Marshmallow is supposed to do: 


  When external storage media is adopted, it’s formatted and encrypted to only work with a single Android device at a time. Because the media is strongly tied to the Android device that adopted it, it can safely store both apps and private data for all users.
  from: https://source.android.com/devices/storage/adoptable.html


Motorola's website is more specific:


  Once a card has been formatted as internal storage,  both your device internal storage and the card will show up as “device storage” under storage settings, and you will be able to  move applications which were in internal storage to the card. Moving an application, its media files, obb files, and data to the card. Moving applications to the card can be done from application settings (settings->apps->select application->change storage location)
  from: https://motorola-global-portal.custhelp.com/app/answers/prod_answer_detail/a_id/109134/p/1449,9582


For example, I've moved Mortal Kombat X (~1.3GB) to the SD card and the majority of its data is in an .obb file sitting in internal storage in /data.

This doesn't make sense because in an app's AndroidManifest.xml the developer must specify the android:installLocation manifest attribute in order for an app to even be allowed to move to an external SD card. But in this case, it wouldn't matter since the SD card is seen by Android as if it were internal storage so it shouldn't have any issues installing there. 

Why is my internal storage still being used?
As mentioned in the comments of the question, this is by design.

According to the docs:


  Apps can be placed on adopted storage media only when the developer has indicated support through the android:installLocation attribute. New installs of supported apps are automatically placed on the storage device with the most free space, and users can move supported apps between storage devices in the Settings app.


In Nougat+, we could even force most app to be movable even without the developers support by toggling Force allow apps on external switch inside developer options.

See here for more: https://www.reddit.com/r/GalaxyS7/comments/5qi1mj/with_nougat_now_we_can_finally_transfer_90_of_the/