I have a Samsung Galaxy Tab S2 and after the 6.0.1 update the SD Card becomes inaccessible after the screen locks while I was accessing it. For example, if I'm playing music files off of it any music player apps freeze shortly after the screen blanks and will not respond until I do a force stop on them. It's not app specific. Multiple player apps do the same thing. At that point ES File Explorer just spins trying to access the card. If I do nothing further, the tablet eventually crashes and will not start again until I remove the SD card.
Everything was working fine before the update. I could start a music player doing shuffle play of mp3s on the card and it would continue to run fine after the screen locked.