Hello,
I have only a Tip, because I work on Windows 10 and I haven’t this issue. If not help, sorry for spam 
If you already have an another application (Keil or something) where is also installed/used same tool, then is a chance there is a collision between versions.
I had an old Git app already installed and after an update of the MbedStudio, where was probably instaled new version of the Git app, I was unable to import from github, until I uninstaled the old git version.
The Git was probably called from ProgramFiles via a system path, instead of from folders for MbedStudio. That issue (about Git) was fixed in Version 0.8.0 of MbedStudio.
BR, Jan