I believe it was Kit-Kat that killed the SD... Google in all of its wisdom decided that transferring files and accessing SD cards was bad and they killed it in Kit-Kat but I thought they fixed it in or by Marshmallow.
I'm seeing advice in other threads that say you need to give specific apps permission to read and write to SD. Sounds like you can go into Settings>applications>permissions and there will be a permission for read/write...?