I have no idea... me I use the defaut binding 'z-h' that works fine. The only reason I would see, it would be because you have mapped this '' shortcut to something in vim (it's common to use this shortcut for moving to the left splitted window for instance)... are you sure you have nothing map for this in your vimrc?
I Can't understand why the shortcut doesn't work when I run the ranger in NeoVim. Shortcut is binded to showing hidden files in ranger .