I created a private share called MyShare via the UI. I granted read/write access only to the admin user but not to any other users. In users I created a user called testuser and it by default has readwrite to the Public share and everything underneath. I then connected to my new share on my Mac and moved some files into share.
On remote access setup - I added remote access to testuser and got a new code. On WD2go I added my device using the new code for testuser. I am only able to see the Public Share and not the new private folder.
I went back into remote access and got a new code for the admin user. I added the device again to WD2go on my iPhone. The new code replaced the previous device - because only one user is allowed per device via the WD2go app (or so it seems).
With the new access code I can see both the public share and my newly created private share with files in it.
If you are not doing something similar to the steps that I outline above - then you may have done something incorrectly.
Also - a while back - there was some type of security fix in one of the firmware updates for the MBL - which I believe corrected a similar access issue to the one you are describing. Make sure you are on the latest firmware 02.10.09-124 - and then try again.