sdcard appears empty for sshdroid, samba fileshare etc, but not for total commander
Just three words: 'supersu namespace separation'. I use SuperSU as root access management tool on my device, which has an option for "namespace separation". I missed the point that this option must be disabled for my firmware.


Open SuperSU application (if you don't have it, then the solution is not applicable to you)
Go to Preferences tab
Scroll down to 'Namespace separation' option and uncheck it
Reboot the device.


This solved the issue on my device.