Can not select /sdcard or /storage/emulated/0 as root
If i clear application data it defaults to /storage/emulated/0 LineageOS (Android 7.1.2), 2.18 from f-droid. When i used Android 6 /storage/emulated/0 was also not available, but /sdcard was.

Also expecting this to be mitigated with my upcoming update with newer storage code. (Currently only github project is updated and not fdroid or Play Store.) If the device doesn't use it then it may still have this problem. The old storage code has some issues there. I will unlikely fix those. I'm already doing more than I wanted to do.
This issue is posted with Android 7. I've tested on Android 8.0 with it working great now. I do have a 7.1.1 device working well enough still and will be testing on that soon.
Addition:
Couldn't test. Client just won't connect to my test device for an unknown reason and not debugging it.
But, I did notice that the sd card on 7.1.1 was able to read and write so this may have been fixed previously anyway or the device flagged in the issue had a problem.