Why has the Move to SD button disappeared

[AC Question]

I have a Galaxy S5 Neo, and up until recently its worked perfectly. I attempted to listen to some music I had stored on an SD card and all of a sudden, i was being told the files were not compatible (id been listening to this music on the phone for over a year at this point). When i tried to replace the music via PC, it just wasnt working properly. So i bought a new SD card but it had the same issue. Music is pretty important to me so i decided to pay for spotify premium and save my favourite albums to the phone but the internal storage is pretty much non existent so I went to application manager to move the spotify app to SD card (something i had done with many apps in the past) and the button is just gone?

 

[Tim1954]

The devs write the code for their apps which decides if the app can be moved to sd or not. If not, the move to sd will be either greyed out or not be there.... Evidently that app cannot be moved.