[Android Q&A, Help & Troubleshooting] davewpy:
On a clean CM14.1 install - no issue.

On a clean CM14.1 install with OpenGApps pico - no issue.

On a clean CM14.1 install with OpenGApps Super with gapps-config - problem appears.

The apps are creating files on /data/media/0 aka /storage/emulated/0 with media_rw:media:rw:600.

Current (manually fixed) permissions:

oneplus2:/data/media/0 # ls -lah
total 86K
drwxrwx--- 19 media_rw media_rw 4.0K 2016-11-29 03:48 .
drwxrwx--- 4 media_rw media_rw 4.0K 1970-01-27 08:50 ..
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Alarms
drwxrwxr-x 4 media_rw media_rw 4.0K 2016-11-29 01:28 Android
drwxrwxr-x 4 media_rw media_rw 4.0K 2016-11-28 23:15 DCIM
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Downloads
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Movies
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Music
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Notifications
drwxrwxr-x 2 media_rw media_rw 4.0K 1970-01-27 11:17 Open-GApps
drwxrwxr-x 3 media_rw media_rw 4.0K 2016-11-29 02:42 Pictures
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Podcasts
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Ringtones
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-28 23:44 SMSBackupRestore
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 TWRP
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Telegram
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 WhatsApp
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 cmupdater
oneplus2:/data/media/0 #

Creating a folder and a file using an app called FX:

oneplus2:/data/media/0 # ls -lah
total 96K
drwxrwx--- 20 media_rw media_rw 4.0K 2016-11-29 03:49 .
drwxrwx--- 4 media_rw media_rw 4.0K 1970-01-27 08:50 ..
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Alarms
drwxrwxr-x 4 media_rw media_rw 4.0K 2016-11-29 01:28 Android
drwx------ 2 media_rw media_rw 4.0K 2016-11-29 03:16 CameraZOOM
drwxrwxr-x 4 media_rw media_rw 4.0K 2016-11-28 23:15 DCIM
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Downloads
-rw------- 1 media_rw media_rw 3 2016-11-29 03:49 File from FX.txt
drwx------ 2 media_rw media_rw 4.0K 2016-11-29 03:49 Folder from FX
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Movies
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Music
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Notifications
drwxrwxr-x 2 media_rw media_rw 4.0K 1970-01-27 11:17 Open-GApps
drwxrwxr-x 3 media_rw media_rw 4.0K 2016-11-29 02:42 Pictures
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Podcasts
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Ringtones
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-28 23:44 SMSBackupRestore
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 TWRP
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 Telegram
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 WhatsApp
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 02:42 cmupdater

Taking a picture...

oneplus2:/data/media/0 # ls -lah DCIM/Camera
total 778K
drwxrwxr-x 2 media_rw media_rw 4.0K 2016-11-29 03:50 .
drwxrwxr-x 4 media_rw media_rw 4.0K 2016-11-28 23:15 ..
-rw------- 1 media_rw media_rw 1.4M 2016-11-29 03:50 IMG_20161129_035027.jpg
oneplus2:/data/media/0 #

I tested on another device and this never happened. Have not been able to properly share documents for the past 3 days and I've never wiped and installed ROMs so many times ever before. :(

Should I clean flash to official OnePlus 2 OOS? If someone would be so kind enough to point me the way in troubleshooting this, it would be much appreciated.