[Xiaomi Mi 5s ROMs, Kernels, Recoveries, & Other De] Schrauber601:
internal storage write access issue

Dear developer,

I still can't figure out, why no app can write to the internal storage. For example: The stock camera app can take a picture ad create an empty file (0 byte). I can't create folder/files with "ES File Explorer" or similar or put files via MTP on my phone. As root, all this works. Most of my apps working normal (if no storage access is needed). My phone is/was encrypted (PIN).

environment:

MI5s 128GiB, data is ext4 formatted

TWRP 3.2.2-0-capricorn installed before update from 14.1 to this

capricornCNFirmware-8.4.26 (installed once just before updating)

lineage-15.1-20180806-nightly-capricorn-signed

open_gapps-arm64-8.1-nano-2010807

SuperSU-v2.82-201705271822 (tried today w/o rooting - same issues)

I cleared 'system' before flashing the Los image and GApps.

mount output:

rootfs on / type rootfs (ro,seclabel,size=1804340k,nr_inodes=451085)
tmpfs on /dev type tmpfs (rw,seclabel,nosuid,relatime,size=1882180k,nr_inodes=470545,mode=755)
devpts on /dev/pts type devpts (rw,seclabel,relatime,mode=600)
none on /dev/memcg type cgroup (rw,relatime,memory)
none on /dev/cpuctl type cgroup (rw,relatime,cpu)
none on /dev/cpuset type cgroup (rw,relatime,cpuset,noprefix,release_agent=/sbin/cpuset_release_agent)
none on /dev/bfqio type cgroup (rw,relatime,bfqio)
adb on /dev/usb-ffs/adb type functionfs (rw,relatime)
proc on /proc type proc (rw,relatime,gid=3009,hidepid=2)
sysfs on /sys type sysfs (rw,seclabel,relatime)
selinuxfs on /sys/fs/selinux type selinuxfs (rw,relatime)
debugfs on /sys/kernel/debug type debugfs (rw,seclabel,relatime)
tracefs on /sys/kernel/debug/tracing type tracefs (rw,seclabel,relatime)
pstore on /sys/fs/pstore type pstore (rw,seclabel,relatime)
/dev/block/sde39 on /system type ext4 (ro,seclabel,relatime,discard,data=ordered)
/dev/block/sde38 on /vendor type ext4 (ro,seclabel,relatime,discard,data=ordered)
none on /acct type cgroup (rw,relatime,cpuacct)
tmpfs on /mnt type tmpfs (rw,seclabel,relatime,size=1882180k,nr_inodes=470545,mode=755,gid=1000)
/data/media on /mnt/runtime/default/emulated type sdcardfs (rw,nosuid,nodev,noexec,noatime,fsuid=1023,fsgid=1023,gid=1015,multiuser,mask=6,derive_gid)
/data/media on /mnt/runtime/read/emulated type sdcardfs (rw,nosuid,nodev,noexec,noatime,fsuid=1023,fsgid=1023,gid=9997,multiuser,mask=23,derive_gid)
/data/media on /mnt/runtime/write/emulated type sdcardfs (rw,nosuid,nodev,noexec,noatime,fsuid=1023,fsgid=1023,gid=9997,multiuser,mask=7,derive_gid)
none on /config type configfs (rw,relatime)
/dev/block/sda14 on /cache type f2fs (rw,lazytime,seclabel,nosuid,nodev,noatime,background_gc=on,no_heap,user_xattr,inline_xattr,acl,inline_data,inline_dentry,flush_merge,extent_cache,data_flush,mode=adaptive,active_logs=6,alloc_mode=reuse,fsync_mode=posix)
/dev/block/sda12 on /persist type ext4 (rw,seclabel,nosuid,nodev,noatime,data=ordered)
/dev/block/sde32 on /dsp type ext4 (ro,context=u:object_r:adsprpcd_file:s0,nosuid,nodev,relatime,data=ordered)
/dev/block/sde35 on /firmware type vfat (ro,context=u:object_r:firmware_file:s0,relatime,uid=1000,gid=1000,fmask=0337,dmask=0227,codepage=437,iocharset=utf8,shortname=lower,errors=remount-ro)
/dev/block/sde26 on /bt_firmware type vfat (ro,context=u:object_r:bt_firmware_file:s0,relatime,uid=1002,gid=3002,fmask=0337,dmask=0227,codepage=437,iocharset=utf8,shortname=lower,errors=remount-ro)
/dev/block/dm-0 on /data type ext4 (rw,seclabel,nosuid,nodev,noatime,noauto_da_alloc,data=ordered)
/dev/block/loop0 on /su type ext4 (rw,seclabel,noatime,data=ordered)
tmpfs on /storage type tmpfs (rw,seclabel,relatime,size=1882180k,nr_inodes=470545,mode=755,gid=1000)
/data/media on /storage/emulated type sdcardfs (rw,nosuid,nodev,noexec,noatime,fsuid=1023,fsgid=1023,gid=1015,multiuser,mask=6,derive_gid)
tmpfs on /storage/self type tmpfs (rw,seclabel,relatime,size=1882180k,nr_inodes=470545,mode=755,gid=1000)

Is "/mnt/runtime/write/emulated" GID=9997 (everybody) correct?

Some ls -lZ output:

drwxrwx--- 4 media_rw media_rw u:object_r:media_rw_data_file:s0 4096 1970-03-30 14:27 media
lrwxrwxrwx 1 root root u:object_r:mnt_user_file:s0 19 2018-08-07 12:02 /storage/self/primary -> /storage/emulated/0
lrwxrwxrwx 1 root root u:object_r:rootfs:s0 21 1970-01-01 01:00 sdcard -> /storage/self/primary
drwxrwx--x 28 root sdcard_rw u:object_r:sdcardfs:s0 4096 2018-08-08 11:48 0
drwxrwx--x 2 root sdcard_rw u:object_r:sdcardfs:s0 4096 2017-06-25 13:50 obb

I tried to connect a USB-stick. Every step I do with 'Total Commander' with USB-Stick-Plugin I get a dialog "USB-Stick Plugin | GOOGLE PLAY RESPONSE: not connected", but it creates a folder and I can copy files to it.

What can I do - what's wrong with my "clean" installation?