I can’t think of anything special on the device. It’s a standard Cyanogenmod release, nothing is customized.
Could it be related to the new permission model on Android 6.0 ?
I’ve also seen various problems with accessing external storage from android applications throughout the web. It seems starting with Android 4.4, applications needs to request write access to external storage.
With adb, connected as a simple user, I can’t access the storage:
····shell@hammerheadcaf:/ $ id
····uid=2000(shell) gid=2000(shell) ····groups=2000(shell),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats)context=u:r:shell:s0
····shell@hammerheadcaf:/ $ ls -alFh /storage/emulated/0
····ls: .: Permission denied